Toxicity of Alternatives to Chlorofluorocarbons: HFC-134a and HCFC-123 (1996)

Prepared by

S. Channel, D. Dodd, J. Fisher, M. George, J. Lipscomb, J. McDougal, A. Vinegar, and J. Williams

Armstrong Laboratory

Toxicology Division and Toxic Hazards Research Unit

Wright-Patterson Air Force Base

Hydrochlorofluorocarbon (HCFC) 123 is used primarily as a foam-blowing agent, as a refrigerant, and as an ingredient in cleaning solvents. The Air Force is considering the use of HCFC-123 as a fire extinguishant, replacing Halon 1211. Halon 1211 has been used as a fire extinguishant in streaming systems, where the extinguishant is manually discharged through a nozzle of small portable units that are commonly found in industry, military, and office settings. Jarabek et al. (1994) reviewed the process of searching for CFC substitutes with HCFC-123 as a specific example.

Personnel with potential military occupational exposure to

HCFC-123 as a fire extinguishant include maintenance personnel (crew chiefs) responding to aircraft fires on the flight line or in indoor structures, such as aircraft hangars, and trained fire fighters responding to alarms. The fire-fighter-exposure scenario deals with military personnel who don appropriate fire-fighting gear, including respirators, immediately before fighting fire. Thus, the exposure scenario of concern in setting emergency exposure guidance levels (EEGLs) involves the emergency situation where maintenance personnel attempt to put out a fire without the appropriate fire-fighting equipment. The exposure duration of concern involves a 1-min period to simulate personnel discharging either the entire contents of a small (1- or 3-lb) extinguisher or the partial contents of a large (150-lb) extinguisher while attempting to put out an aircraft fire (usually an engine fire) from upwind of the fire (C. Kibert, Tyndall Air Force Base, Fla., personal commun., 1994).

The potential for repeated exposures to a streaming agent such as Halon 1211 has been estimated to be minimal. According to D. Vickers (Tyndall Air Force Base, Fla., personal commun., 1994), there are about three aircraft fires per Air Force wing per year. An average wing has 60 crew chiefs assigned; therefore, the probability that a crew chief will experience a fire in any one year is 1 in 20 or 0.05. The probability of experiencing two fires in a 20-year career is 0.1887 or about 1 in 5, according to the multiplication rule:

The probability of experiencing three fires in a career is about 1 in 20. Probabilities of experiencing more than three fires are much less. The expectation of any crew chief for number of fires over a 20-year career is 1.

Brashear et al. (1992) exposed F344 and Sprague-Dawley rats to HCFC-123 and detected the metabolites 2-chloro-1,1,1-trifluoroethane (HCFC-133a) and 2-chloro-1,1-difluoroethylene in the liver immediately following exposure. The most abundant metabolite in the urine was TFA. Additionally, Harris et al. (1991) and Martin et al. (1992) exposed rats to 1% HCFC-123 and, via ¹⁹F nuclear magnetic resonance spectrometry, observed the formation of reactive TFA intermediates with liver proteins. These newly formed TFA proteins have been implicated in halothane-induced hepatitis (Harris et al., 1991; Owen and Van der Veen, 1986). (See Attachment 2 for toxicity information on halothane and a comparison of HCFC-123 and halothane.)

Both oxidative and reductive pathways participate in the metabolism of HCFC-123. The reductive pathway occurs only under conditions of very low oxygen tension and would not be expected to be a common route in man (Dodd et al., 1993). It begins with reductive dehalogenation to produce a radical intermediate that either can accept a hydrogen atom from a protein or a phospholipid to form HCFC-133a or can lose a fluorine to yield chlorodifluoroethylene. The oxidative pathway catalyzed by cytochrome P-450 produces a dichloro geminal halohydrin, which is unstable, and releases HCl to form trifluoroacetylchloride, which is hydrolyzed to TFA. These pathways are similar to those for the structur-

ally related compound halothane where TFA, HCFC-133a, and chlorodifluoroethylene have been detected as metabolites (Stier, 1964; Mukai et al., 1977; Sharp et al., 1979). It is unknown whether different isoforms of P-450 are responsible for differential metabolism of HCFC-123 or halothane via the oxidative or reductive pathways. The metabolism of halothane and several other halogenated hydrocarbons has been shown to be catalyzed primarily by the P-450IIE1 isoform. This isoform is expressed differentially in the sexes and is induced by such substances as ethanol, acetone, and isoniazid.

The metabolism of HCFC-123 in vitro has been determined by using rat liver microsomes and aerobic conditions. Preliminary results of in vitro rat microsomal studies conducted at Wright-Patterson Air Force Base by C.S. Godin (personal commun.) indicate that the rate of formation of TFA from HCFC-123 is approximately 0.2 nmol/nmol P-450 per min. Urban and Dekant (1993) compared the metabolism of HCFC-123 and halothane in rat and human liver microsomes. For rat liver microsomes, the rate of formation of TFA from HCFC-123 was 3.1 nmol/mg per 20 min and the formation of TFA from halothane was 2.1 nmol/mg per 20 min. For human liver microsomes, rates of formation of TFA from HCFC-123 ranged from 5.4 to 41.9 nmol/mg per 20 min.

No literature citations were found of studies on HCFC-123 exposure to humans.

Attachment 3 of this supporting doumentation provides an out-

line of acute-toxicity results for HCFC-123 and lists the references.

Acute Toxicity and CNS Depression. Potential toxicity during acute exposure to HCFC-123 includes severe central nervous system (CNS) depression and cardiac sensitization. The liver might be a target organ of concern following acute exposure to HCFC-123. All animal species exposed to HCFC-123 show CNS depression, and in rodent LC₅₀ studies, death is attributed to severe CNS depression. Rodent LC ₅₀ values are comparable across species and average 37,000 ppm for exposures of 4- to 6-hr durations (Darr, 1981; Hall and Moore, 1975; Coate, 1976; Waritz and Clayton, 1966). For exposures of ≤30 min duration in mice, concentrations of 74,000 ppm and higher produced mortality (Burns et al., 1982; Raventos and Lemon, 1965); 40,000 to 50,000 ppm was nonlethal. The lowest HCFC-123 concentration causing CNS depression (inactivity or altered response to auditory stimuli) in rats is 5,000 ppm (Mullin, 1976). A concentration of 1,000 ppm does not produce narcosis in rats or dogs (Mullin, 1976; Trochimowicz and Mullin, 1973).

Cardiac Sensitization. The standard cardiac-sensitization protocol as defined by Reinhardt et al. (1971) has been applied to Halon and many of the Halon-replacement chemicals. [This protocol has been reviewed in detail in Chapter 2 of this report.] Briefly, the male beagle dogs are exposed to vapor concentrations of the test substance diluted in air via face mask following a “priming” dose of epinephrine (0.008 mg/kg given i.v. in 1 mL saline over 9 sec; rate = 50 µg/kg/min). After 5 min of exposure to the test agent, a “challenge” dose of epinephrine is administered under the same conditions as the priming dose. Cardiac activity is followed by electrocardiography and “marked” responses are tabulated. A “marked” response is defined as “those arrhythmias considered to pose a serious threat to life or which ended in cardiac arrest.”

The only data available for HCFC-123 are reported by Trochimowicz and Mullin (1973). They used a “staircase-method” modifi-

cation of the standard protocol to study vapor concentrations (% vol/vol in air) and obtained an estimate of the EC₅₀. A summary of the results follows:

Statistical interpretation of the data indicated an EC₅₀ of 1.9% with a 95% confidence interval of 1.29% ≤ EC₅₀ ≤ 2.82%. These authors suggest that the unusually high percentage of fatal marked responses might reflect the nature of the staircase modification, which requires more test concentrations above the initial estimate of the EC₅₀. Additionally, the extremely rapid onset of ventricular fibrillation, within 3 to 6 sec of the challenge dose, implies an effect that is specific to the compound itself.

The table on the following page summarizes the cardiac-sensitization results for other chemicals under the same experimental conditions.

Repeated exposures do not change the cardiac-sensitization effects of chemicals. Beck et al. (1973) studied the pharmacological actions, including cardiac arrhythmias and cardiac sensitization, of bromochlorodifluoromethane (BCF) in laboratory animals. BCF was selected as a prototype of halogenated hydrocarbons that produces CNS and cardiac effects. The authors (Beck et al., 1973) concluded from their results that cardiac sensitization occurred at the end of very brief exposures to BCF, but the concentration of BCF has to be high. Exposure (5 min/day, 3 days/week for 4 weeks) to BCF at a concentration that caused minimal cardiac sensitization did not make the heart more susceptible to epinephrine arrhythmias.

Malignant Hyperthermia. HCFC-123 has not been tested for its potential to produce malignant hyperthermia in the Pietrain malignant hyperthermia-susceptible pig model.

Hepatotoxicity. The potential for acute HCFC-123 exposure to produce hepatotoxicity in the guinea pig has been evaluated recently at Wright-Patterson Air Force Base (G. Marit, A. Vinegar, and M. George, unpublished material, 1994). The use of a guinea pig model for examining the mechanisms of acute liver injury produced by halothane (Lunam et al., 1985; Lind et al., 1987) has received considerable attention, because the spectrum of liver injury observed in guinea pigs exposed to anesthetic concentrations (1%) of halothane resembles that observed in nonfatal halothane hepatitis in humans (Lunam et al., 1989). Exposure-related liver alterations were observed in guinea pigs exposed for 4 hr to HCFC-123-vapor concentrations of 3%, 2%, 1%, or 0.1%. In agreement with the results of Lunam et al. (1985, 1989) and Lind et al. (1987), there were wide variations in individual sensitivity based on lesion morphology, severity, and incidence. Liver lesions observed in guinea pigs exposed to 3% or 2% HCFC-123 included centrilobular necrosis and degeneration and were comparable to those observed in guinea pigs exposed to 1% halothane (G. Marit, A. Vinegar, and M. George, unpublished material, 1994). Hepatic lesions observed in guinea pigs exposed to 1% or 0.1% HCFC-123 were mild in severity (altered hepatocytes and lymphoid infiltrates) and multifocal or random in distribution. All liver lesions observed in guinea pigs exposed for 4 hr to HCFC-123 at concentrations of 0.1-3% were considered reversible.

Attachment 3 of this supporting documentation provides an outline of repeat-exposure toxicity results for HCFC-123 and lists the references.

For evaluating general toxicity due to repeated exposure to HCFC-123, the 90-day (Malley, 1990a) and 1-year (Malley, 1990b) studies in rats are thorough and well documented. The exposure concentrations used in these studies were 0 (control), 300, 1,000, and 5,000 ppm. Malley states that a no-observed-effect level (NOEL) was not established in these studies owing to exposurerelated changes in select serum chemistry values and hepatic betaoxidation enzyme activity at all HCFC-123 concentrations.

The liver is a target organ of toxicity following HCFC-123 exposure. Hepatic degenerative changes, including hypertrophy, clear cytoplasm, and necrosis with inflammatory cell infiltrates, were observed in the 90-day dog study at an exposure concentration of 10,000 ppm (Crowe, 1978). However, rats exposed to the same HCFC-123 concentration for 90 days (Crowe, 1978), or even higher concentrations for shorter exposure periods (Lewis, 1990; Kelly, 1989), did not produce similar hepatic effects, although some indexes of liver toxicity (liver weight, hepatocellular hypertrophy and fatty vacuolation, and hepatic peroxisomal activity) were observed to be of greater magnitude or incidence when compared with control values. For a no-observed-adverse-effect level (NOAEL), dogs exposed to 1,000 ppm for 90 days did not have liver damage.

A study on the oncogenic potential of HCFC-123 in rats has been completed recently (Malley, 1992). Exposure concentrations were 5,000, 1,000, 300, and 0 (control) ppm. Consistent with the 90-day and 1-year studies (Malley, 1990a,b), exposure-related changes were observed in select serum chemistry values (e.g., triglyceride, glucose, and cholesterol) and in hepatic beta-oxidation enzyme activity at all HCFC-123 concentrations. In this study, a NOEL was not achieved using clinical chemical values —lower body weight and body-weight gain, increased incidence of neoplastic and non-neoplastic morphological changes, and higher hepatic betaoxidation activity—at all concentrations. The tumor incidences of concern were increases in benign hepatocellular adenomas or hepatic cholangiofibromas or both, increases in benign pancreatic acinar cell adenomas, and increases in interstitial cell adenoma in

the testes. Diffuse retinal atrophy was increased in all test groups of both males and females. Also noteworthy was the observation that the survival index was higher in HCFC-123-exposed rats in comparison to control rats.

The potential for HCFC-123 to produce developmental toxicity or reproductive toxicity has not been evaluated fully. Developmental toxicity studies in rabbits (Bio-Dynamics, 1989a,b) and rats (Culik and Kelly, 1976; IBT, 1977) indicate that a concentration of 5,000 ppm is a NOAEL for the development of terata, but maternal toxicity effects were not studied in dogs exposed to HCFC-123 at 500 ppm. Only minimal toxicity was observed at 500 ppm in the Cullick and Kelly (1976) study. No evidence for maternal or fetal toxicity was seen in the IBT (1977) study. Testicular effects were observed in rats exposed to HCFC-123 at 20,000 ppm for 4 weeks (Kelly, 1989), although testicular lesions have not been observed in rats exposed to lower HCFC-123 concentrations (Kelly, 1976, 1989; Crowe, 1978; IBT, 1977; Malley et al., 1990a,b). The observation of benign testicular tumors in the rat 2-year bioassay might be coincidental.

Fire training exercises have been performed routinely by Air Force personnel. In 1991, the Air Force directed the Midwest Research Institute (MRI) to assess the hazards associated with the inhalation of selected Halon-replacement compounds and determine the fate and effects of the Halon-replacement-chemical and jet-fuel combustion products. To accomplish this directive, a detailed air-monitoring survey of representative training-exercise test burns was conducted by using Halon-replacement candidates, including HCFC-123, and by burning jet fuel. This fire-fighter training scenario differs from anticipated flight-line exposures to the crew chief in two ways: (1) fire fighters wore protective gear and used respirators, and (2) they applied the fire-fighting agent at a

slow rate to avoid putting out the fire immediately. Selected results from this study (Midwest Research Institute, 1992) follow.

Training exercises of test burns with HCFC-123 as the extinguishant involved the use of either 130 lb of HCFC-123 applied at a flow rate of 2.5 lb/sec to an approximate 4-min (fire duration) 75-ft³ fuel fire (extinguishment not achieved) or 99 lb of HCFC-123 applied at a flow rate of 4.7 lb/sec to an approximate 30-sec (fire duration) fuel fire (extinguishment achieved).

Analysis of the air samples in the breathing area of the fire fighter indicated that concentrations of HCFC-123 ranged from 0.2 to 5.4 ppm. Ground (ankle-height) concentrations of HCFC-123 were approximately 10-fold higher than head-height concentrations. Of comparative interest, plume-air-sample concentrations of HCFC-123 ranged from 0.18 to 180 ppm, and downwind-air-sample concentrations of HCFC-123 ranged from 0.17 to 129 ppm.

In the MRI study, risks to fire fighters were examined with respect to the generation of toxic-fuel and extinguishant combustion products (e.g., the acid gases HCl, HBr, HF, and COF₂) that were analyzed in the test burns, but occupational risks were not calculated from measured concentrations of HCFC-123 per se. Using acid gases as an index for HCFC-123 and jet-fuel combustion products, the MRI investigators found that the limits in the model of immediately dangerous to life or health (IDLH) set for the individual acid gases were exceeded up to 50 meters downwind of the fire, and the IDLH limit for the combined acid gases was exceeded up to 100 meters downwind of the fire.

Recently, the U.S. Environmental Protection Agency contracted with Meridian Research, Inc., to assess occupational exposures to Halon substitutes used for fire protection (Meridian Research Inc., 1992). HCFC-123 was selected for analysis in this assessment. The purpose of these studies was to assess the concentrations of the agents from an indoor release. Noteworthy results from this analysis follow.

Three scenarios that represented worst-case exposure situations were considered for modeling:

1. Use of a 1-lb extinguisher in a single-person office.

2. Use of a 3-lb extinguisher in a two- or three-person office.

3. Use of a 150-lb extinguisher inside a large enclosed area (e.g., aircraft hangar).

Occupational exposures were expressed as instantaneous peak concentrations, 30-min-average concentrations, and 8-hr time-weighted-average (TWA) concentrations. Meridian Research used a gas volume equivalent value of 1.97 for the modeling of HCFC-123 concentrations; thus, the concentration of HCFC-123 calculated to be needed to fight a fire was twice as much as that of Halon 1211. In the single-person office scenario where 1 lb of HCFC-123 was discharged in 10 sec in a 960-ft³ area, the peak concentration was 4,827 ppm, the 30-min average was 161 ppm, and the 8-hr TWA was 10 ppm. In the two- or three-person office scenario where 3 lb of HCFC-123 was discharged in a 1,780 ft³ area, the peak concentration was 1,970 ppm, the 30-min average was 66 ppm, and the 8-hr TWA was 4.1 ppm.

The third exposure scenario included two hangar sizes (336,000 and 3,000,000 ft³) and two air-exchange rates (one-half or three air changes per hour (ACH)) for the 3-min discharge of approximately 128 lb of HCFC-123. To account for the differences between exposures near the fire and away from the fire, additional analyses were done. Depending on area size and ACH, the HCFC-123 peak concentrations near the fire ranged from 920 to 25,472 ppm and the 30-min averages ranged from 92 to 2,516 ppm. Away from the fire, the HCFC-123 peak concentrations ranged from 99 to 912 ppm and the 8-hr TWAs ranged from 6.2 to 373 ppm. In this example, the 8-hr TWA was redefined to account for a 2-hr absence of the worker soon after the discharge of the HCFC-123 cylinder.

As indicated previously, potential occupational military expo-

sure to HCFC-123 as a fire extinguishant is expected to be brief with low probability of repeated exposures. The selection of a 1-min exposure for establishing an EEGL is appropriate and represents a “typical” emergency exposure scenario outdoors or indoors where the area can be evacuated after use of a fire extinguisher. For HCFC-123, the end points of pharmacological or adverse effects considered for establishing an EEGL are cardiac sensitization, anesthesia or CNS-related effects, malignant hyperthermia, and hepatotoxicity.

Cardiac sensitization was chosen as the most sensitive end point because of the potent sensitizing effect of this chemical and similar chemicals in the epinephrine-challenged dog model. The EC₅₀ for HCFC-123 was determined to be 1.9% for a 5-min exposure (Trochimowicz and Mullin, 1973). We believe that 1.9% should be considered the human NOEL for a 1-min exposure to HCFC-123 in humans on the basis of the dog cardiac-sensitization model. We believe that this concentration is very unlikely to cause arrhythmias under the proposed-use scenario for the following reasons:

• Actual duration of exposure for humans would be one-fifth the duration of the dog-test exposure.

• Tissue concentrations in humans would be much less in a 1-min exposure than those in the 5-min exposure of dogs.

• Arrhythmia-producing concentrations in humans would be much less than those in the dog exposure because an actual exposure scenario would not be in the presence of a supraphysiological i.v. bolus of epinephrine (i.e., a dose that is about 10 times that of a adrenal release in humans during times of stress).

The dog cardiac-sensitization test is very conservative. It incorporates priming and supraphysiological challenge doses of epinephrine. The original purpose of this test was to rank chemicals that might be cardiac sensitizers and not to set regulatory limits for humans. In this test, the epinephrine dose is maximized to be just below the point where it causes arrhythmias by itself. There-

fore, the 1-min EEGL of 1.9% derived on the basis of the dog cardiac-sensitization test is considered conservative.

A recent study sponsored by the Air Force provides additional support for the recommendation for the 1-min EEGL to be 1.9% for HCFC-123 (Vinegar et al., 1995). Using this study to extrapolate assumes that the blood concentration at the NOEL (1% for 5 min) would be safe (Attachment 4). Using the slope of the relationship between blood concentration and exposure concentration for a 1-min exposure (Figure 1), the NOEL blood concentration (9.0 mg/L, range 2.7-18) would be equivalent to a 1-min exposure to 1.9% HCFC-123 in the atmosphere. Because 1.9% is the 5-min EC50 in the dog assay (a very conservative test) and because it can be extrapolated from the 5-min NOEL, 1.9% is suggested as the most appropriate 1-min EEGL.

FIGURE 1 Extrapolation from the measured blood concentration at the NOEL. The 1-min line connects blood concentrations measured after a 1-min exposure to 1% and 5% HCFC-123.

Studies in laboratory animals indicate that HCFC-123 is approximately three times less potent than halothane for producing anesthesia. Concentrations of approximately 1% halothane produce anesthesia. A subanesthetic halothane exposure of 4,000 ppm for 30 min causes transient impairment in mental performance in humans. In HCFC-123 inhalation studies, mild CNS depression is observed in rats exposed (for 6 hr) to 5,000 ppm, but these effects are rapidly reversible upon cessation of exposure. Dogs exposed to HCFC-123 at 10,000 ppm for 5 min show signs of CNS depression. In studies performed by Clark and Tinston (1982) involving acute exposure of rats and dogs to a series of halogenated hydrocarbons, CNS effects and cardiac sensitization occur at the same concentration, and the more potent the chemical was in producing CNS effects, the more potent it was in producing cardiac sensitization. For selected halogenated hydrocarbons, it would be difficult to choose one of these biological end points over the other as the most sensitive measure of pharmacological or toxicological effect. For the purposes of the EEGL, it was assumed that anesthetic effects would occur at the concentration that could cause cardiac sensitization.

Malignant hyperthermia (MH) was ruled out as an end point because there is no evidence that HCFC-123 causes it, and halothane causes MH in only a very small portion of the population. If HCFC-123 caused MH and the incidence was similar that caused by halothane (1 in 50,000), it would not be as much of a concern as cardiac sensitization.

Hepatotoxicity due to HCFC-123 was observed in guinea pigs exposed once for 4 hr to HCFC-123 concentrations of 3%, 2%, 1%, or 0.1%. However, the selection of cardiac sensitization as the most sensitive end point for a 1-min EEGL is still considered appropriate on the basis of the following rationales:

• The guinea pig appears to be a sensitive model when compared with other species, such as the rat and human, for inducing hepatotoxicity with halothane (and presumably HCFC-123). The

guinea-pig model's relevancy in assessing the health hazard to humans has not been evaluated fully.

• The liver lesions produced by HCFC-123 were considered reversible and showed no indication of producing permanent damage morphologically or functionally.

• The proposed mechanism that causes halothane to produce hepatitis is immunologically based. Although an association between TFA-protein adducts and liver toxicity exists, a dose-response relationship between formation of TFA-protein adduct and induction of immune responses in sensitized individuals does not exist. Without dose-response relationships, risk assessments of immune-mediated hepatitis for humans are not possible.

• No information is available on the potential for HCFC-123 to produce liver toxicity in guinea pigs at short (<30 min) exposure times. The impact of a 1-min exposure would be expected to be of no consequence.

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Munson, E.S., and W.K. Tucker. 1975. Doses of epinephrine causing arrhythmia during enflurane, methoxyflurane and halothane anaesthesia in dogs. Can. Anaesth. Soc. J. 22(4):495-500.

Mukai, S., M. Morio, K. Fujii, and C. Hanaki. 1977. Volatile metabolites of halothane in the rabbit. Anesthesiology 47:248-251.

Nakao, M., K. Fujii, H. Kinoshita, O. Yuge, and M. Morio. 1991. Aerobic dehalogenation of halothane showing different substrate dependency from anaerobic dehalogenation in liver microsomes of guinea pigs . Hiroshima J. Med. Sci. 40(1):23-28.

Nelson, T.E., M. Lin, and P. Volpe. 1991. Evidence for intraluminal Ca⁺⁺ regulatory site defect in sarcoplasmic reticulum from malignant hyperthermia pig muscle. J. Pharmacol. Exp. Ther. 256:645-649.

Owen, A.D., and B.W. Van der Veen. 1986. Perspectives in the pathogenesis of halothane-induced hepatitis. S. Afr. Med. J. 69:807-810.

Petruscak, J., and R.B. Smith. 1974. Safety of epinephrine infiltration during halothane anesthesia: A review. Anesth. Progress 21(3):76-81.

Rasmussen, B.A., and L.L. Christian. 1976. H blood types in pigs as predictors of stress susceptibility. Science 191:947-948.

Raventos, J. 1956. The action of fluothane—A new volatile anaesthetic. Br. J. Pharmacol. 11:394-410.

Raventos, J. and P.G. Lemon. 1965. The impurities in fluothane:

Their biological properties. Br. J. Anaesth. 37:716-737.

Reinhardt, C.F., A. Azar, M.E. Maxfield, P.E. Smith, and L.S. Mullin. 1971. Cardiac arrhythmias and aerosol “sniffing.” Arch. Environ. Health 22:265-279.

Sharma, P.L. 1970. Effect of oxprenolol on adrenaline-evoked ventricular arrhythmias in dogs anaesthetized with halothane in oxygen. Br. J. Anaesth. 42:961-966.

Sharp, J.H., J.R. Trudell, and E.N. Cohen. 1979. Volatile metabolites and decomposition products of halothane in man . Anesthesiology 50:2-8.

Stier, A. 1964. Trifluoroacetic acid as a metabolite of halothane. Biochem. Pharmacol. 13:1544.

Summary of the National Halothane Study. 1966. J. Am. Med. Assoc. 197:775.

Trochimowicz, H.J. 1975. Tabular Summary of Halon 1301 Toxicity in Animals and Man. Haskell Laboratory.

Trochimowicz, H.J., and L.S. Mullin. 1973. Cardiac Sensitization Potential (EC₅₀) of Trifluorodichloroethane. Rep. 132-73. Haskell Laboratory.

Urban, G., and W. Dekant. 1993. The CFC-substitute 1,1-dichloro2,2,2-trifluoroethane is primarily oxidized by cytochrome P-45011E1. Toxicologist 13:431.

Vanik, P.E., and H.S. Davis. 1968. Cardiac arrhythmias during halothane anesthesia. Anesth. Analg. 47(3):299-307.

Vinegar, A., D. Dodd, D. Pollard, R. Williams, and J. McDougal. 1995. Pharmacokinetics of HCFC-123 in Dogs. Technical Report No. AL/OE-TR-1995-0025. Armstrong Laboratory , Wright-Patterson Air Force Base.

Waritz, R.S., and J.W. Clayton. 1966. Acute Inhalation Toxicity (FC-123). Report No. 16-66. Haskell Laboratory.

Warner, L.O., and T.P. Beach. 1984. Halothane and children: The first quarter century. Anesth. Analg. 63(9):838-840.

Williams, C.H., M.D. Shanklin, H.B. Hedrick, et al. 1977. The fulminant hyperthermia stress syndrome: Genetic aspects, hemodynamic and metabolic measurements in susceptible and normal pigs. Pp. 113-140in Malignant Hyperthermia , J.A. Aldrete and B.A. Britt, eds. New York: Grune and Stratton.

Zink, J., B.I Sasyniuk, and P.E. Dresel. 1975. Halothane-epinephrine induced cardiac arrhythmias and the role of heart rate. Anesthesiology 43(5):548-555.

MATERIAL SAFETY DATA SHEET

GENETRON^®123

1. CHEMICAL PRODUCT AND COMPANY IDENTIFICATION

PRODUCT NAME: GENETRON^® 123

OTHER/GENERIC NAMES: 1,1-Dichloro-2,2,2-Trifluoroethane

PRODUCT USE: Refrigerant

MANUFACTURER: AlliedSignal, Inc. Fluorocarbons 101 Columbia Road P.O. Box 1053 Morristown, NJ 07962

FOR MORE INFORMATION CALL: (Monday-Friday, 9:00am-4:30pm)Eastern Standard Time Product Safety Department (201) 455-4157

IN CASE OF EMERGENCY CALL: (24 Hours/Day, 7 Days/Week) (201) 455-2000

2. COMPOSITION/INFORMATION ON INGREDIENTS

INGREDIENT NAME CAS # WEIGHT %

Dichlorotrifluoroethane 306-83-2 100

Trace impurities and additional material names not listed above may also appear in the Regulatory Information section (#15) towards the end of the MSDS. These materials may be listed for local “Right to Know” compliance and for other reasons.

3. HAZARDS IDENTIFICATION

EMERGENCY OVERVIEW: Colorless, volatile liquid with ethereal and faint sweetish odor. Non-flammable material. Overexposure may cause dizziness and loss of concentration. At higher levels, CNS depression and cardiac arrhythmia may result from exposure. Vapors displace air and can cause asphyxiation in confined spaces. At higher temperatures, (> 250°C), decomposition products may include Hydrochloric Acid (HCl), Hydrofluoric Acid (HF), and carbonyl halides such as phosgene.

POTENTIAL HEALTH HAZARDS:

SKIN: Irritation would result from defatting action on tissue.

EYES: Liquid contact can cause irritation which may be severe. Mist may irritate.

INHALATION: Genetron^® 123 have a relatively low order of acute toxicity. When oxygen levels in air are reduced to 12-14% by displacement, symptoms of asphyxiation, loss of coordination, increased pulse rate and deeper respiration will occur. In repeated exposure tests with animals, changes were noted in liver functions and lipid production at level above 100 ppm. At higher levels, cardiac arrythmia may occur.

INGESTION: Although not a likely route of exposure, discomfort in the gastrointestinal tract would

result from the rapid evaporation (boiling) of the material, and consequent evolution of gas. In addition, some of the effects of inhalation would be expected.

DELAYED EFFECTS: No delayed effects of a single exposure have been identified. Delayed effects of multiple exposure are seen in animal studies by the formation of late developing benign tumors.

Ingredients found on one of the OSHA designated carcinogen listsare listed below.

Ingredient Name NTP Status IARC Status OSHA List

*No ingredients listed in this section*

4. FIRST AID MEASURES

SKIN: Promptly flush skin with water until all chemical is removed. Get medical attention if irritation is present.

EYE: Immediately flush eyes with large amounts of water for at least 15 minutes, lifting eyelids to facilitate irrigation. Get medical attention if symptoms persist.

INHALATION: Immediately remove to fresh air. If breathing has stopped give artifical respiration. Use oxygen as required, provided a qualified operator is available. Call a physician. Do not give epinephrine (adrenaline).

INGESTION: Ingestion is an unlikely route of exposure and is not likely to be hazardous. It may cause discomfort due to its low boiling point. Do not induce vomiting unless directed to do so by a physician. Consult a physician.

ADVICE TO PHYSICIAN: Because of possible disturbances of cardiac rhythm, catecholamine drugs such as epinephrine, should be used with special caution only in situations of emergency life support. Treatment of overexposure should be directed at the control of symptoms and the clinical conditions.

5. FIRE FIGHTING MEASURES

FLAMMABLE PROPERTIES:

FLASH POINT: N.A. - No flash point

FLASH POINT METHOD: ASTM D 1310-67 and ASTM D 56-82

AUTOIGNITION TEMPERATURE: 770°C (1418°F)

UPPER FLAME LIMIT (Volume % in air): None

LOWER FLAME LIMIT (Volume % in air): None

FLAME PROPAGATION RATE (Solids): Not applicable

OSHA FLAMMABILITY CLASS: Not applicable

EXTINGUISHING MEDIA:

Use any standard agent - choose the one most appropriate for type of surrounding fire (material itself is not flammable).

UNUSUAL FIRE AND EXPLOSION HAZARDS:

Contact with certain reactive metals may result in explosive or exothermic reactions under specific conditions (e.g., very high temperatures and/or appropriate pressures and in the presence of oxygen). High temperatures may result in formation of toxic or corrosive products, such as halogen acids, carbonyl halides (e.g. Phosgene). See Reactivity section.

SPECIAL FIREFIGHTING PRECAUTIONS/INSTRUCTIONS:

Firefighters should wear self-contained, NIOSH-approved breathing apparatus for protection against possible toxic decomposition products. Proper eye and skin protection should also be provided. Use water spray to keep fire-exposed containers cool and to suppress vaporization.

6. ACCIDENTAL RELEASE MEASURES

IN CASE OF SPILL OR OTHER RELEASE: (Always wear recommended personal protective equipment.) Evacuate unprotected personnel. Protected personnel should remove ignition sources and shut off leak, if without risk, and provide ventilation. Unprotected personnel should not return until air has been tested and determined safe, including low-lying areas.

Spills and releases may have to be reported to Federal and/or localauthorities. See the Regulatory Information section (#15) regardingreporting requirements.

7. HANDLING AND STORAGE

NORMAL HANDLING: (Always wear recommended personal protective equipment.) Avoid breathing vapors and liquid contact with eyes, skin or clothing. Do not puncture or drop cylinders or expose them to open flame or excessive heat. Use authorized containers only. Follow standard safety precautions for handling and use of drums.

STORAGE RECOMMENDATIONS:

Store in a cool, well-ventilated area of low fire risk. Storage in subsurface locations should be avoided. Keep containers out of direct sun. If storage temperature exceeds boiling point of 82°F, the container will develop pressure. COOL BEFORE REMOVING PRODUCT.

8. EXPOSURE CONTROLS/PERSONAL PROTECTION

ENGINEERING CONTROLS:

Provide local exhaust at filling zones and areas where leakage is probable. Mechanical (General) ventilation may be adequate for other operating and storage areas. Concentration of G-123 should be monitored and kept below the recommended levels in work areas.

PERSONAL PROTECTIVE EQUIPMENT:

SKIN PROTECTION:

Wear protective, impervious gloves and clothing with an outer layer of MYLAR^®-coated Durafab (2nd choices: PVA or neoprene), if prolonged or repeated contact with liquid is anticipated. Remove and wash clothing promptly. Any non-impervious clothing should also be promptly removed when contaminated and washed before reuse.

EYE PROTECTION:

For normal conditions, wear safety glasses. Where there is reasonable probability of liquid contact, wear chemical safety goggles.

RESPIRATORY PROTECTION:

None generally required for adequately ventilated work situations. For accidental or non-ventilated situations, where concentrations are above recommended PEL (10 ppm), use a self-contained, NIOSH-approved breathing apparatus or supplied air respirator. For escape: use the former or a NIOSH-approved gas mask with organic vapor canister.

ADDITIONAL RECOMMENDATIONS:

Wear impervious boots in case of spillage or leakage, or if there is the probability of repeated or prolonged contact with liquid product. High dose-level warning signs are recommended for areas of potential exposure. Provide eyewash stations and quick-drench shower facilities at convenient locations. For tank cleaning operations, see OSHA regualtions.

EXPOSURE GUIDELINES: (Guidelines exist for the following ingredients)

Ingredient Name ACGIH TLV OSHA PEL Other Limit

Dichlorotrifluoroethane None None *10 ppm TWA

* = Limit established by AlliedSignal for internal use.

** = Workplace Environmental Exposure Level (AIHA).

*** = Biological Exposure Index

Other exposure limits for the decomposition products normally associated with product use are as follows:

Hydrogen Fluoride: ACGIH TLV: 3 ppm ceiling

9. PHYSICAL AND CHEMICAL PROPERTIES

APPEARANCE: Clear colorless liquid and vapor.

PHYSICAL STATE: G-123 is a liquid at room temperature.

MOLECULAR WEIGHT: 152.9

CHEMICAL FORMULA: CHCl₂CF₃

ODOR: Faint ethereal odor

SPECIFIC GRAVITY: (Water = 1.0) 1.47 gram/cc @ 70°F

SOLUBILITY IN WATER: (Weight %) 0.21% (wt) @ 70°F

pH: Neutral

BOILING POINT: 27.9°C (82.2°F) @ 760 mm Hg

MELTING POINT: −107°C(−160.6)°F

VAPOR PRESSURE: 11 psia (20°C) (68°F)

VAPOR DENSITY: (Air = 1.0) 5.3

EVAPORATION RATE: Greater than 1 Compared to: CCl₄

% VOLATILES: % Volatiles by volume @ 20°C (68°F) = 100

FLASH POINT: N.A. - No flash point

(Flash point method and additional flammability data are found in section 5.)

10. STABILITY AND REACTIVITY

NORMALLY STABLE? (Conditions to Avoid)

Sources of high temperatures, such as lighted cigarettes, flames, welding cutting torches or unit heaters should be avoided to prevent formation of toxic and/or corrosive by-products. By analogy with other HCFC's welding or burning on equipment containing G-123 with or without oxygen may result in explosion.

INCOMPATIBILITIES:

Freshly abraded aluminum surfaces (may cause strong exothermic reaction). Chemically active metals for example, sodium, potassium, calcium, L/C powdered aluminum, magnesium or zinc.

HAZARDOUS DECOMPOSITION PRODUCTS:

Halogens, halogen acids, and possibly carbonyl halides, such as phosgene may be formed. These are toxic and corrosive.

After G-123 has been exposed to lubricated oils, alcohols, polyols or other hydrocarbons at temperatures in excess of 100°F, the composition should be monitored for reaction products, particularly G-133a. Reaction products may be toxic.

HAZARDOUS POLYMERIZATION?

Will not occur.

11. TOXICOLOGICAL INFORMATION

IMMEDIATE (ACUTE) EFFECTS:

LC₅₀ - 4 HR (rat): 32,000 ppm

Cardiac Sensitization Threshold (dog): 20,000 ppm

DELAYED (SUBCHRONIC and CHRONIC) EFFECTS:

Chronic:

At 300 ppm, benign testicular and pancreatic tumors developed in a statistically significant number of animals at or near the end of the study. Retinal atrophy was increased in the test animals. Liver tumors were found in test animals at concentrations at and above 300 ppm. None of the effects were life threatening or life shortening.

OTHER DATA:

A retarded rate of weight gain and lower pup weights were found in a two generation rat reproductive study. These effects were seen at inhalation concentration above 100 ppm for animals exposed through out the test.

Six genetic assay were run five of which were negative. The sixth, chromosome aberration of human lymphocytes, was weakly positive.

12. ECOLOGICAL INFORMATION

Aquatic Toxicity

Green Algae LC₅₀ = 96.6

Daphnia Magna LC₅₀ = 17.3

Rainbow Trout LC₅₀ = 55.5

Degradability (BOD):

Not pertinent.

Octanol Water Partition Cofficient: Unknown

13. DISPOSAL CONSIDERATIONS

RCRA:

Is the unused product a RCRA hazardous waste if discarded? Not a hazardous waste.

If yes, the RCRA ID number is: Not applicable

OTHER DISPOSAL CONSIDERATIONS: (Disposer must comply with federal, state, and local disposal or discharge laws.) Disposal of waste G-123 may be subject to federal regulations. Users should review their operations, then consult with appropriate regulatory agencies before discharging or disposing of waste material. Disposal by a licensed waste disposal company may be necessary.

The information offered here is for the product as shipped. Use and/or alterations to the product such as mixing with other materials may sisnificantly change the characteristics of the material and alter the RCRA classification and the proper disposal method.

14. TRANSPORT INFORMATION

US DOT HAZARD CLASS: Not regulated

US DOT ID NUMBER: Not applicable

For additional information on shipping regulations affecting this material, contact the information number found on the first page.

15. REGULATORY INFORMATION

TOXIC SUBSTANCES CONTROL ACT (TSCA):

TSCA INVENTORY STATUS: Listed

OTHER TSCA ISSUES: None

SARA TITLE III/CERCLA:

RQs and TPQs:

“Reportable Quantities” (RQs) and/or “Threshold Planning Quantities” (TPQs) exist for the following ingredients.

SARA/CERCLA SARA EHS

Ingredient RQ(lbs) TPQ(lbs)

*No ingredients listed in this section*

Spills/releases resulting in the loss of any ingredient at or aboveits RQ requires immediate notification to the National Response Center(1-800-424-8802) and to your Local Emergency Planning Committee.

SECTION 311 HAZARD CLASS: IMMEDIATE PRESSURE

SARA 313 TOXIC CHEMICALS:

The following ingredients are SARA 313 “Toxic Chemicals”. CAS 's and wt.% are found in section*.

Ingredient Comment

Dichlorotrifluoroethane None

STATE RIGHT TO KNOW:

In addition to the ingredients found in section 2, the following are listed for state right-to-know purposes:

Ingredient Wt.% Comment

No ingredient listed in this section.

ADDITIONAL REGULATORY INFORMATION:

WARNING

DO NOT VENT TO THE ATMOSPHERE. TO COMPLY WITH PROVISIONS OF THE U.S. CLEAN AIRACT, ANY RESIDUAL MUST BE RECOVERED.

CONTAINS GENETRON^®123, A HCFC, A SUBSTANCE WHICH HARMS PUBLIC HEALTH AND ENVIRONMENT BYDESTROYING OZONE IN THE UPPER ATMOSPHERE. DESTRUCTION OF THE OZONELAYER CAN LEAD TO INCREASED ULTRAVIOLET RADIATION WHICH, WITH EXCESSEXPOSURE TO SUNLIGHT, CAN LEAD TO AN INCREASE IN SKIN CANCER ANDEYE CATARACTS.

WHMIS CLASSIFICATION (CANADA):

Not determined

FOREIGN INVENTORY STATUS:

EINECS Number: 2061903

16. OTHER INFORMATION

CURRENT ISSUE DATE: September 1994

PREVIOUS ISSUE DATE: January 1992

CHANGES TO MSDS FROM PREVIOUS ISSUE DATE ARE DUE TO THE FOLLOWING:

Added AlliedSignal PEL and Toxicity information

New Format

OTHER INFORMATION: HMIS Classification 2-0-0

MSDS Number: GTRN-0013

Current Issue Date: September 1994

Halothane has been used as an anesthetic agent in humans and other animals for over 30 years. Use in recent years has declined because of the introduction of new volatile anesthetics.

Acute exposure of humans to halothane has been associated with cardiac sensitization, malignant hyperthermia, or hepatotoxicity. Each of these manifestations of toxicity will be discussed in detail to better assess the potential hazard of acute HCFC-123 exposure.

The LC₅₀ for 30-min inhalation of halothane in mice is 2.8% and the AC₅₀ (anesthetic) is 0.86% (Raventos, 1956). The same author reports that dogs exposed to concentrations of halothane between 2% and 4% achieve full surgical anesthesia within 2 to 5 min. Inhalation of 3% halothane for 1 hr did not stop respiration; however, concentrations of 3.5% and 4.0% produced severe CNS depression and respiratory arrest at 45 to 60 min and 20 to 30 min, respectively.

Halothane concentrations of approximately 1% are commonly used as general anesthetics in clinics. However, volunteers exposed for 30 min to a subanesthetic halothane concentration of 0.4% might experience amnesia and impairment in mental performance and manual dexterity (Cook et al., 1978). Recovery from these impairments is rapid.

The initial characterization of halothane was reported by Raven

tos in 1956. Cardiac sensitization in dogs was measured by administrating increasing i.v. doses of epinephrine at 20 min intervals. In unpremedicated dogs exposed to 1.0-1.2% halothane, a mean dose of epinephrine of 8.8 µg/kg administered at a rate of 1.5 µg/ kg/min was required to produce ventricular tachycardia (n = 13 dogs, 1 death). It is important to note that the author reported no observable occurrences of electrocardiographic irregularities to have occurred in dogs or monkeys during anesthetic induction (2-3% halothane) or maintenance (0.8-1.2% halothane) without epinephrine injection. This suggests that endogenous epinephrine secretion under these conditions was insufficient to produce sensitization.

Hall and Norris (1958) refined Raventos' findings by direct i.v. injection into the vena cava of halothane-anesthetized dogs. This modification was an attempt to administer an “instantaneous ” dose directly to the myocardium. In one group of 17 dogs exposed to 1.36% halothane, the mean fatal dose of epinephrine was 5.1 ± 5.1 µg/kg. The extreme variability in the epinephrine dose necessary to produce fatal ventricular fibrillation in 13 of 17 dogs suggested that other factors may have altered individual susceptibility. The importance of the route of administration was seen in the inability to produce fatal arrhythmias with intramuscular epinephrine injection of amounts 159 times greater than the i.v. doses. Data from these and other later studies are summarized in the following table.

These results emphasize the importance of both total dose and the rate of administration of that dose in producing arrhythmia. Unfortunately, these studies were not designed to test several concentrations of halothane exposure with a fixed epinephrine challenge dose.

Halothane has been used as a general anesthetic in humans for over 30 years. Much of the literature consists of epidemiological retrospective case-control studies or individual case reports. Derivation of incidence values is possible with epidemiological studies. However, confounding factors, such as inexact exposure concentrations, premedications, ventilation rates, and disease state, combine to add uncertainly to the analysis. Two examples demonstrate typical data:

Arrhythmia during surgery is common. Studies have reported incidence of arrhythmia ranging from 17.9% (Vanik and Davis, 1968) to 61.7% (Kuner et al., 1967) for patients under all types of anesthesia. It is reasonable to conclude that some fraction of the incidence of halothane-induced arrhythmias might be due to factors other than simple exposure to halothane. If true, the risk of spontaneous cardiac arrhythmia from exposure to halothane is best described as quite low.

There are studies that describe concurrent use of halothane with epinephrine in humans. Many are summarized in an excellent review by Petruscak and Smith (1974). They cite one particular study that described the i.v. dose of epinephrine necessary to induce arrhythmia in a group of 20 unselected patients. Under 1.4-2.5% halothane anesthesia, a mean i.v. dose of 7.2 µg/min was necessary to induce arrhythmia in 12 of 20 subjects (60%). When epinephrine was increased to 10 µg/min, the severity of the arrhythmias increased. No fatalities were reported, and presumably the arrhythmias subsided.

In humans, inhalation anesthetics, primarily halothane, can induce skeletal muscle rigidity, hypermetabolism, and high fever, which can cause irreversible tissue damage and death. These effects, called malignant hyperthermia (MH) syndrome, occur in a select group of genetically predisposed individuals. An abnormality in the Ca²⁺ release channel of skeletal muscle sarcoplasmic reticulum might account for the disorder in humans (MacLennan and Phillips, 1992). There is a corresponding condition in swine that leads to stress-induced deaths (porcine stress syndrome) and devalued meat products (pale, soft, and exudative pork) (Nelson et al., 1991).

The mechanism of halothane-induced changes has been explored to the extent that the parent compound is believed to be

the vector in MH. Little in the literature suggests that any halothane metabolite, such as trifluoroacetic acid, chlorodifluoroethylene, or chlorotrifluoroethane, could be responsible for MH.

The literature is replete with epidemiological, anecdotal, and clinical case studies on halothane and MH in humans. No true dose-response studies have addressed MH in humans. Dose-response data applied to halothane have been extracted from studies in which the parent compound or metabolites have been implicated in such diseases as halothane-induced hepatitis in humans and inhalant-induced cardiac sensitization in dogs (Trochimowicz and Mullin, 1973).

A study was done on the dose-response relationship of halothane and MH in pigs (McGrath et al., 1984). Purebred Pietrain MH-susceptible pigs (n = 102) were subjected to halothane (0%, 1%, 2%, 3%, 4%, and 5%) in oxygen (5 L/min). The number of pigs in each group exhibiting muscle rigidity (a positive reaction for MH) and the reaction time in seconds were recorded, as were the number of deaths resulting from MH. Mortality was not affected by halothane concentration. Halothane concentration did markedly affect the number of MH-positive reactions and the reaction times. False-negative reactions were apparent in pigs at halothane concentrations <3%. Increasing the halothane concentration incrementally from 0% to 5% significantly decreased (p < 0.05) reaction times between treatment groups. The reductions in reaction times that occurred in the pigs given the 3%, 4%, and 5% halothane concentrations (62.1, 56.2, and 50.0), although significant (p < 0.05), would indicate that 3% halothane would be the effect level in this highly sensitive model.

The following table summarizes halothane test procedures used by other investigators using the MH-positive end point of muscle rigidity:

The critical research goal for MH in humans is directed at the advanced detection of anesthesic-induced disease, not dose-response or dosimetry studies. Statistical data collected before efforts to circumvent anesthetic-induced MH reactions in humans indicate that the incidence of MH episodes was about 1 in 15,000 anesthetic uses in children 's hospitals and 1 in 50,000 in adult hospitals (Britt, 1991). There are a number of epidemiological studies of

the effect of waste anesthetic vapors on operating room personnel. Once again, these studies fail to identify a dose-response relationship.

Soon after halothane was introduced into clinical practice, reports of unexplained jaundice appeared after anesthesia (Brown and Sipes, 1977). A nationwide retrospective study (National Halothane Study, 1966) indicated that this jaundice occurred rarely (approximately 1:30,000 administrations). Due to repeated failure of laboratory animal studies to reveal a direct hepatotoxic effect of halothane, allergic or hypersensitivity reactions were implicated. At present, this implication has gained considerable attention as a viable mechanism of halothane-induced hepatotoxicity. Support for this hypothesis comes from the observation that a reactive intermediate of halothane metabolism binds with liver proteins, and the resulting product— trifluoroacetyl- (TFA) protein adduct—acts as a neoantigen, which can elicit an immune response (Kenna et al., 1987). Patients diagnosed as having halothane hepatitis produce antibodies that recognize TFA-protein adducts (Kenna et al., 1987; Hubbard et al., 1988). Thus, these newly formed TFA-protein adducts have been implicated in halothane-induced hepatitis (Harris et al., 1991; Owen and Van der Veen, 1986).

To determine and evaluate the mechanisms of acute liver injury produced by halothane, a laboratory animal model was developed by using the guinea pig (Lunam et al., 1985; Lind et al., 1987). The spectrum of liver injury observed in guinea pigs exposed to halothane resembles that observed in nonfatal halothane hepatitis in humans (Lunam et al., 1989). Lunam et al. (1989) reported that 22 of 40 guinea pigs exposed to 1% halothane in 21% oxygen showed hepatic necrosis, either mild or severe. The remaining 18 guinea pigs showed no liver damage. Previous results by Lunam et al. (1985) indicated that the lesion produced by halothane is transient

in nature. Although hepatic lesions were observed several days after exposure, 1 week after exposure no guinea pig livers showed signs of histopathology (0 of 10). Of 10 guinea pigs exposed to 1% halothane and evaluated 2 days following exposure, four had marked liver damage, three had mild liver damage, and three had no liver damage. Seventy percent had liver damage. Overall, the incidence of liver damage in the study was 62% (40 of 65 guinea pigs). Additional studies by Lind et al. (1990) indicate that the presence of TFA-protein adducts is associated with halothane hepatotoxicity in the guinea pig.

For rodents, anesthetic or lethal concentrations of HCFC-123 are higher when compared with halothane. Results of mouse studies by Raventos (1956) and Raventos and Lemon (1965) follow:

Test results of studies using either halothane or HCFC-123 for cardiac-sensitization potential were presented previously. The study designs were not similar because of the different amounts of epinephrine used as challenge doses, but comparisons can be made. At the average exposure to halothane of about 10,000 ppm, the epinephrine administration rates were one order of magnitude

less than the 50 µg/kg/min needed to produce similar arrhythmia with HCFC-123. In addition, HCFC-123 exposure concentrations at which the sensitization was observed are greater by a factor of two (2-4% HCFC-123 versus 1% halothane). Also noteworthy is the observation that the epinephrine dose rate to produce cardiac irregularities is higher in humans than in dogs. Thus, the cardiacsensitization potential of chemicals tested with the dog model might provide a conservative estimate for humans.

Malignant hyperthermia studies have not been performed with HCFC-123; therefore, inferences on the relationship between HCFC-123 and MH are based on the study results with halothane (discussed previously).

The guinea pig model for halothane-induced liver toxicity was investigated for its potential to produce hepatotoxicity with HCFC-123 (G. Marit, A. Vinegar, and M. George, unpublished material, 1994). Single 4-hr exposure concentrations of 2% or 3% HCFC-123 produced hepatotoxic effects similar to a halothane exposure concentration of 1%. In addition, guinea pigs exposed to either 0.1% or 1% HCFC-123 had minimal-to-mild liver lesions that were similar to those observed in guinea pigs exposed to 0.1% halothane (Lind et al., 1992). These preliminary (unpublished) results of the guinea pig study with HCFC-123 indicate that halothane is more potent than HCFC-123 in producing hepatotoxicity in the guinea pig model.

Britt, B.A. 1991. Pp. 179-292 in Thermoregulation: Pathology, Pharmacology and Therapy, E. Schonbaum and P. Lomax, eds. New York: Pergamon Press.

Brown, B.R. and I.G. Sipes. 1977. Biotransformation and hepatotoxicity of halothane. Biochem. Pharamacol. 26:2091-2094.

Christian, L.L. 1974. Halothane test for PSS field application. Proc. Am. Assoc. Swine Pract. 6-11.

Cook, T.L., M. Smith, P.M. Winter, J.A. Starkweather, and E.I. Eger II. 1978. Effect of subanesthetic concentrations of enflurane and halothane on human behavior. Anesth. Analg. 57:434-440.

Hall, K.D. and F. Norris. 1958. Fluothane sensitization of dog heart to action of epinephrine. Anesthesiology 19:631-641.

Harris, J.W., L.R. Pohl, J.L. Martin, and M.W. Anders. 1991. Tissue acylation by the chlorofluorocarbon substitute 2,2-dichloro-1,1,1-trifluoroethane . Proc. Natl. Acad. Sci. USA 88:1407- 410.

Hubbard, A.K., T.P. Roth, A.J. Gandolfi, and B.R. Brown. 1988. Halothane hepatitis patients generate an antibody response toward a metabolite of halothane. Anesthesiology 68:791-796.

Kenna, J.G., J. Neuberger, and R. Williams. 1987. Identification by immunoblotting of three halothane-induced liver microsomal polypeptide antigens recognized by antibodies in sera from patients with halothane-associated hepatitis. J. Pharmacol. Exp. Ther. 242:733-740.

Kuner, J., V. Enescu, F. Utsu, E. Boszormenyi, H. Bernstein, and E. Corday. 1967. Cardiac arrhythmias during surgery. Dis. Chest 52:580.

Lind, R.C., A.J. Gandolfi, B.R. Brown, and P.M. Hall. 1987. Halothane hepatotoxicity in guinea pigs. Anesth. Analg. 66:222-228.

Lind, R.C., A.J. Gandolfi, and P.M. Hall. 1990. Covalent binding of oxidative biotransformation intermediates is associated with halothane hepatotoxocity in guinea pigs. Anesthesiology 73:208-1213.

Lind, R.C., A.J. Gandolfi, and P.M. Hall. 1992. Subanesthetic halothane is hepatotoxic in the guinea pig. Anesth. Analg. 74:559-563.

Lunam, C.A., M.J. Cousins, and P.M. Hall. 1985. Guinea pig model of halothane-associated hepatotoxicity in the absence of enzyme induction and hypoxia. J. Pharmacol. Exp. Ther. 232(3):802-809.

Lunam, C.A., P.M. Hall, and M.J. Cousins. 1989. The pathology of

halothane hepatotoxicity in a guinea pig model: a comparison with human halothane hepatitis. Br. J. Exp. Pathol. 70:533-541.

Mabry, J.W., L.L. Christian, and D.L. Kuhlers. 1983. Prediction of susceptibility to the porcine stress syndrome. J. Hered. 74:23-26.

MacLennan, D.H., and M.S. Phillips. 1992. Malignant hyperthermia. Science 256:789-793.

McGrath, C.J., W.E. Rempel, P.B. Addis, et al. 1981a. Acepromazine and droperidol inhibition of halothane-induced malignant hyperthermia (porcine stress syndrome) in swine. Am. J. Vet. Res. 42:195-198.

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Nelson, T.E., M. Lin, and P. Volpe. 1991. Evidence for intraluminal Ca⁺⁺ regulatory site defect in sarcoplasmic reticulum from malignant hyperthermia pig muscle. J. Pharmacol. Exp. Ther. 256:645-649.

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Petruscak, J., and R.B. Smith. 1974. Safety of epinephrine infiltration during halothane anesthesia: A review. Anesth. Progress 21(3):76-81.

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1. Hamster

   100% mortality: 31,000 ppm (4 hr)

   0% mortality: 26,000, 22,000, 14,000,10,000 ppm (all 4 hr)

   LC₅₀: 28,400 ppm (4 hr)

   Sedation observed in all exposure groups

   Source: Darr, 1981

2. Mouse

   67% mortality: 80,000 ppm (18 min)

   No deaths, but anesthesia: 40,000 to 50,000 ppm (30 min)

   Source: Burns et al., 1982

   LC_50: 74,000 ppm (30 min)

   AC₅₀ (AC, anesthetic concentration): 24,000 ppm (30 min)

Source: Raventos and Lemon, 1965

Mouse micronucleus genotoxicity test:

2,000, 6,000, 18,000 ppm × 6 hr

Toxicity in all groups, but no micronuclei in bone-marrow erythrocytes

Source: Müller and Hofmann, 1988

2. Rat

   LC₅₀: 32,000 ppm (4 hr)

   4-hr dose, ppm	Mortality
   55,000	6/6
   52,500	6/6
   42,100	4/6
   33,700	3/6
   32,000	3/6
   20,700	0/6

   CNS depression observed at all doses

   Source: Hall and Moore, 1975

   LC₅₀: 52,575 ppm (6 hr)

   Dose, mg/L (ppm)	Time	Mortality
   766.67 (122,517)	20 min	10/10
   660.42 (105,538)	24 min	10/10
   261.42 (41,776)	6 hr	4/10
   236.00 (37,714)	6 hr	1/10
   234.17 (37,421)	6 hr	2/10
   144.72 (23,127)	6 hr	0/10
   48.61 (7,768)	6 hr	0/10
   0	6 hr	0/10

   Anesthesia or inactivity in all exposure groups except 0 ppm

Source: Coate, 1976

LC₅₀: 35,000 ppm (4 hr)

Source: Waritz and Clayton, 1966

LD_lo (gavage in corn oil; 20-50% solutions): 9,000 mg/kg

Dose, mg/kg	Mortality
15,024	1/1
13,934	1/1
11,000	1/1
9,000	1/1
7,500	0/1
5,000	0/1
3,400	0/1
2,250	0/1

Clinical signs in animals dosed at 3,400 mg/kg and above

Source: Henry and Kaplan, 1975

LD₅₀ (dermal): >2,000 mg/kg (24-hr occlusion; 2,000 mg/kg was the only dose tested)

Source: Brock, 1988a

CNS depression during exposure at concentrations of 5,000 ppm and higher (1 hr)

No CNS depression at 1,000 ppm (1 hr)

Source: Mullin, 1976

4. Rabbit

   LD₅₀ (dermal): >2,000 mg/kg (24-hr occlusion; 2,000 mg/kg was the only dose tested)

   Source: Brock, 1988b

5. Dog

   CNS depression:

CNS depression during exposure at 10,000 ppm

No CNS depression at 1,000 ppm

Cardiac sensitization EC₅₀: 19,000 ppm (5 min; includes epinephrine, 0.008 mg/kg, iv, challenge immediately before test chemical exposure)

No reaction: 10,000 ppm (3/3)

Marked reaction: 20,000 ppm (4/6) (3 died)

Marked reaction: 40,000 ppm (3/3) (all died)

Source: Trochimowicz and Mullin, 1973

1. General Toxicity

   1. Rat

      2-wk

      10,000 ppm × 6 hr/day × 5 days/wk

      No toxicity, but CNS depression during exposure

      Source: Kelly, 1976

      4-wk

      1,000, 5,000, 10,000,20,000 ppm × 6 hr/day × 5 days/wk

      Dose-related effects: CNS depression during exposure (males and females at 5,000 ppm and above); body-weight-gain decrease (males at 10,000 and 20,000 ppm); relative liver-weight increase (males at 20,000 ppm; females at all doses); cytochrome-P-450 decrease (males at 10,000 and 20,000 ppm; females at all doses); urinary-fluoride increase (males at 20,000 ppm; females at 10,000 and 20,000 ppm); testicular degeneration and hypospermia (6 of 10 males at 20,000 ppm)

      Source: Kelly, 1989

4-wk (males only)

1,000, 5,000, 20,000 ppm × 6 hr/day × 5 days/wk

Dose-related effects: CNS depression during exposure (at 20,000 ppm); body-weight decrease (at all doses); absolute and relative liver-weight increase (at 20,000 ppm); relative testes-weight increase (at all doses); cholesterol decrease (44% at 5,000 ppm; 51% at 20,000 ppm); serum alkaline phosphatase increase (79% at 20,000 ppm); hepatocellular hypertrophy and fatty vacuolation (at all doses); hepatic peroxisome increase (126% at 5,000 ppm; 242% at 20,000 ppm)

Source: Lewis, 1990

90-day

1,000/10,000 ppm × 6 hr/day × 5 days/wk for 90 days

Dose-related effects: CNS depression during exposure (10,000 ppm); body-weight-gain decrease (males and females at all doses); relative liver-weight-increase (males and females at all doses); relative testis- (males), adrenal- (males), kidney- (females), and stomach-(females) weight increases; tracheal lesion (3 of 21 females at 10,000 ppm)

Source: Crowe, 1978

90-day

500, 1,000, 5,000 ppm × 6 hr/day × 5 days/wk for 94 days plus a 30-day recovery period after exposure

Dose-related effects: body-weight-gain decrease (males at 5,000 ppm; females at 1,000 and 5,000 ppm—reversible); relative liver-weight increase (in the high exposure level males and in all three HCFC-123 exposure level females; these increases were dose-related—reversible); initial diagnosis of liver lesions (reversible); diagnosis review indicated incidental lesions

Source: IBT, 1977

90-day

300, 1,000, 5,000 ppm × 6 hr/day × 5 days/wk for 90 days

Dose-related effects: CNS depression during exposure (at 5,000 ppm); serum glucose and triglyceride decreases (males and females at all doses); cholesterol decrease (females at 1,000 and 5,000 ppm); lymphocyte decrease (females at 5,000 ppm); relative liver-weight increase (males and females at 1,000 and 5,000 ppm); absolute liver-weight increase (males at 5,000 ppm); hepatic beta-oxidation-enzyme increase (two-to four-fold increase in males and females at 1,000 and 5,000 ppm)

Source: Malley, 1990a

1-yr

300, 1,000, 5,000 ppm × 6 hr/day × 5 days/wk for 1 yr

Dose-related effects: CNS depression during exposure (at 5,000 ppm); body-weight-gain and food-consumption decreases (males at 5,000 ppm; females at 1,000 and 5,000 ppm); serum glucose and triglyceride decreases (males and females at all doses); cholesterol decrease (males at 5,000 ppm; females at 1,000 and 5,000 ppm); relative liver-weight increase (males and females at 5,000 ppm); hepatic beta-oxidation-enzyme increase (two- to four-fold increase in males at all doses and females at 1,000 and 5,000 ppm) with no change in hepatic cell-proliferation rate; urinary-fluoride increase (males and females at all doses)

Source: Malley, 1990b

2. Dog

   90-day (males only and organ weights were not determined)

1,000, 10,000 ppm × 6 hr/day × 5 days/wk for 90 days

Dose-related effects: CNS depression during exposure (at 10,000 ppm); hematology alterations (at 10,000 ppm); serum SGOT and SGPT increases (at 10,000 ppm); alkaline phosphatase increase (at 1,000 and 10,000 ppm); hepatic degenerative changes including hypertrophy, clear cytoplasm, and necrosis with inflammatory cell infiltration (at 10,000 ppm)

Source: Crowe, 1978

2. Oncogenicity

   1. Rat

      2-year

      300, 1,000, 5,000 ppm × 6 h/day × 5 days/wk for 2 yr

      Dose-related effects:

      Survival-index increase:

      Males	HCFC-123	Females
      26%	0 ppm	23%
      31%	300 ppm	34%
      40%	1,000 ppm	46%
      43%	5,000 ppm	59%

      Select serum chemical increases (e.g., triglyceride, glucose, and cholesterol) and hepatic beta-oxidationenzyme increase (at all doses); NOEL not achieved on the basis lower body weight and body-weight-gain decrease (at all doses), relative liver-weight increase (at 5,000 ppm); increased incidence of neoplastic and non-neoplastic morphological changes and hepatic peroxisomal beta-oxidation increases (at all doses); increased tumor incidences of concern: benign hepatocellular adenomas and/or hepatic cholangiofibromas, benign pancreatic acinar cell adenomas, and interstitial cell adenoma in the testes

Source: Malley, 1992

3. Developmental Toxicity

   1. Rat (impregnated females)

      10,000 ppm × 6 hr/day × 10 gestation days (gestation days 6-15)

      CNS depression during exposure, equivocal fetal toxicity, and no terata

      Source: Culik and Kelly, 1976

      5,000 ppm × 6 hr/day × 10 gestation days (gestation days 6-15)

      Maternal body-weight-gain decrease, no fetal toxicity

      Source: IBT, 1977

   2. Rabbit (impregnated females)

      1,000, 5,000,10,000, 20,000 ppm × 6 hr/day × 13 gestation days (gestation days 6-18) “range-finder study”

      Dose-related effects: maternal body-weight-gain and food-consumption decreases (at all doses); fetal body-weight decrease (at all doses); tail defects (13% at 20,000 ppm)

      Litter-size decrease:

      Mean litter size	Dose, ppm
      8.3	0
      7.3	1,000
      7.4	5,000
      5.5	10,000
      5.8	20,000
      Source: Bio-Dynamics, 1989a

   3. Rabbit (impregnated females)

      500, 1,500, 5,000 ppm × 6 hr/day × 13 gestation days (gestation days 6-18) “definitive study”

Dose-related effects: maternal body-weight-gain and food-consumption decreases (at all doses) and no terata; increased number of resorptions:

Relative incidence	Dose, ppm
1	0
3×	500
4×	1,500
5×	5,000
Source: Bio-Dynamics, 1989b

Bio-Dynamics, Inc. 1989a. An Inhalation Range-Finding Study to Evaluate the Toxicity of CFC 123 in the Pregnant Rabbit. Project No. 88-3303. Bio-Dynamics.

Bio-Dynamics, Inc. 1989b. An Inhalation Developmental Toxicity Study in Rabbits with HCFC 123 . Project No. 88-3304. Bio-Dynamics.

Brock, W.J. 1988a. Acute dermal toxicity study of HCFC-123 in rats. Report No. 577-88. Haskell Laboratory.

Brock, W.J. 1988b. Acute dermal toxicity study of HCFC-123 in rabbits. Report No. 578-88. Haskell Laboratory.

Burns, T.H.S., J.M. Hall, A. Bracken, and G. Gouldstone. 1982. Fluorine compounds in anaesthesia (9). Examination of six aliphatic compounds and four ethers. Anaesthesia 37:278-284.

Coate, W.B. 1976. LC₅₀ of G123 in Rats. Final Report. Project No. M165-162. Hazleton Laboratories America.

Crowe, C.D. 1978. Ninety-Day Inhalation Exposure of Rats and Dogs to Vapors of 2,2-Dichloro-1,1,1-Trifluoroethane (FC-123). Report No. 229-78. Haskell Laboratory.

Culik, R., and D.P. Kelly. 1976. Embryotoxic and Teratogenic Studies in Rats with Inhaled Dichlorofluoroethane (Freon 21) and 2,2-Dichloro-1,1,1-Trifluoroethane (FC-123). Report No. 227-76. Haskell Laboratory.

Darr, R.W. 1981. An acute inhalation toxicity study of fluorocarbon 123 in the Chinese hamster. Report No. MA-25-78-15. Allied Corp. , Morristown, N.J.

Hall, G.T., and B.L. Moore. 1975. 1,1-Dichloro-2,2,2-Triflu-

oroethane. Acute Inhalation Toxicity. Report No. 426-75. Haskell Laboratory.

Henry, J.E., and A.M. Kaplan. 1975. 1,1-Dichloro-2,2,2 trifluoroethane. Acute oral test. Report No. 638-75. Haskell Laboratory.

IBT (Industrial Bio-test Laboratories). 1977. Ninety-Day Inhalation Study and Teratology Study with Genetron 123 in Rats. Report No. 8562-09344. Industrial Bio-test Laboratories , Decatur, Ill.

Kelly, D.P. 1976. Two-Week Inhalation Toxicity Studies (FC-21 and FC-123). Report No. 149-76. Haskell Laboratory.

Kelly, D.P. 1989. Four-Week Inhalation Study with HCFC-123 in Rats. Report No. 229-89. Haskell Laboratory.

Lewis, R.W. 1990. HCFC 123: 28-Day Inhalation Study to Assess Changes in Rat Liver and Plasma. Report No. CTL/T2706. Central Toxicology Laboratory, Imperial Chemical Industries.

Malley, L.A. 1990a. Subchronic Inhalation Toxicity: 90-Day Study with HCFC-123 in Rats . Report No. 594-89. Haskell Laboratory.

Malley, L.A. 1990b. Combined Chronic Toxicity/Oncogenicity Study with HCFC-123. Two-Year Inhalation Toxicity Study in Rats (One-Year Interim Report). Report No. 260-90. Haskell Laboratory.

Malley, L.A. 1992. Combined Chronic Toxicity/Oncogenicity Study with HCFC-123. Two-Year Inhalation Toxicity Study in Rats. Report No. 669-91. Haskell Laboratory.

Müller, W., and T. Hofmann. 1988. HCFC 123 micronucleus test in male and female NMRI mice after inhalation . Report No. 88.1340. Pharma Research Toxicology and Pathology, Hoechst , Hattersheim, Germany.

Mullin, L.S. 1976. Behavioral Toxicity Testing. Fluorocarbon 123. Report No. 941-76. Haskell Laboratory.

Raventos, J., and P.G. Lemon. 1965. The impurities in fluothane: Their biological properties. Br. J. Anaesth. 37:716-737.

Trochimowicz, H.J., and L.S. Mullin. 1973. Cardiac sensitization potential (EC₅₀) of trifluorodichloroethane. Report No. 132-73. Haskell Laboratory.

Waritz, R.S., and J.W. Clayton. 1966. Acute Inhalation Toxicity(FC-123). Report No. 16-66. Haskell Laboratory.

The objective of this study was to evaluate the pharmacokinetic behavior of HCFC-123 in an exposure scenario that mimics the cardiac-sensitization test in dogs and to use the data to support the development of a physiologically based pharmocokinetics model. Specific emphasis was placed on the measurement of blood and tissue samples following exposure of 1% or 5% HCFC-123 for 1-5 min.

Two male beagle dogs per time-point were exposed to HCFC-123 at either 1% or 5% for various exposure durations (Table 1).

Exposure was “nose-only” via a specially adapted canine anesthesia mask equipped with a two-way non-rebreathing valve. The exposure system was designed to provide instantaneous exposure of the dogs to the target concentrations and permit the drawing of blood samples. Blood samples were collected (as applicable) at 0 (pre-exposure), 1, 2, 3, 4, 5, 7.5, 10, 15, 30, 45, and 60 min during exposure and 1, 3, 6, 16, and 31 min after exposure and analyzed for HCFC-123. At the end of the exposure periods, animals were euthanized and samples from selected tissues (heart, liver, fat, and skeletal muscle) were collected as rapidly as possible for analysis of HCFC-123.

The dog nose-only exposure system set up is presented schematically in Figure 1. Liquid HCFC-123 was evaporated by heating a glass reservoir while air passed across the test article surface. The HCFC-123 was first brought to target concentrations in a 500-liter NYU-type inhalation chamber, then supplied to the animal via a sideport. Concentrations in the exposure chamber were monitored with a Miran 1A gas analyzer. Chamber air flow, temperature, relative humidity, and oxygen were monitored as well. Each animal

was exposed individually. The animal was first secured in a sling, and the snout placed in a modified dog anesthesia mask. The snout went through a small hole in a rubber diaphragm to provide a seal. The animal breathed either chamber atmosphere or room air via a valve on the exposure line sideport (Figure 1). The animal breathed the HCFC-123 through a two-way non-rebreathing valve to maintain a unidirectional flow of chemical.

FIGURE 1 Dog nose-only exposure system setup.

A 5.0-cm over-the-needle Teflon catheter was inserted into a saphenous vein. The catheter was attached to a three-way valve so that heparinized saline could be used to flush the catheter. A 3-mL glass syringe was used to draw blood samples. Three ≈ 100-µL samples were place into preweighed headspace vials and reweighed for analysis of HCFC-123 concentration. For tissue sampling, animals were euthanized by lethal injection. The dead animals were transferred as rapidly as possible to a necropsy suite to harvest tissues for HCFC-123 analysis. The intact heart was removed first, followed by samples of fat (perirenal), liver, and skeletal muscle. For each tissue, three subsamples of ≈ 500 mg were weighed and sealed in headspace vials. In general, the entire necropsy procedure was completed in less than 5 min.

Blood and tissue samples were stored in a ≄80°C freezer until analysis. Headspace vials containing blood or standards were loaded onto a Tekmar 7050 static headspace sampler for injection onto a Varian 3700 gas chromatograph. The gas chromatograph was equipped with a 0.53-mm 25-m PoraPlot Q column and an electron capture detector. Tissue samples were first digested with sodium hydroxide solution to release the HCFC-123 into the head-

space. The digestion process occurred within the headspace vial. The digested samples were analyzed in the same manner as the blood. Sample headspace HCFC-123 concentrations were calculated from a standard curve.

The blood and tissue (heart, muscle, liver, and fat) concentrations for all exposure scenarios are given in Table 2 and Table 3, respectively. In animals exposed for 60 min (n = 4), the maximum venous blood concentrations (mean values) were attained within 30 min, with less than a 3% increase over the next 30 min (Figure 2 and Table 2). Animals allowed to recover for 30 min (n = 2) had rapid decreases in the venous blood concentrations within the first 16 min with concentrations approaching the limits of detection by 31 min after exposure (Figure 3 and Table 2).

Figure 4 and Figure 5 are graphs of the triplicate blood concentrations at the early time points for all animals exposed to 1% and 5% HCFC-123, respectively. The experimental design allowed for the sampling of eight animals at 1.0-min during the 1% exposure concentrations. Due to problems in sampling, half of the 1.0-min samples were not available for analysis. The plot of data was tightly clustered, with a gradual increase in the blood concentrations during the first 5-6 min of the 1% exposure. This was not the case for the 5% exposure. The plot of data showed two parallel groupings of data (each a different dog) that increased in concentration from 1 to 5 min. More than two dogs would be required to know the blood concentrations with greater certainty. Difference in behavioral reaction to the 5% exposure concentration between dogs is the most plausible reason for differences in blood concentration.

The rise and fall in tissue concentrations paralleled that of blood. Heart, liver, and muscle tissue appeared to take up HCFC-123 much quicker than fat tissue (Table 3). It should be noted that the concentration of chemical in fat, in animals exposed for 60

min, was two- to three-fold higher than the other tissues as expected. The solubility of HCFC-123 in fat (partition coefficient = 52.9) is approximately 25 times greater than muscle (2.3), liver (1.9), or heart (2.5) tissues. Subsequently, the washout of chemical in fat tissue was much slower than any other tissue. In general, the blood and tissue concentrations of HCFC-123 both increased with exposure time and increasing concentration.

FIGURE 5 5% HCFC-123 dog blood levels for all exposed animals.

Analysis of the pharmacokinetics from this study facilitates extrapolating the 5-min cardiac-sensitization level to the 1-min level. As expected, both blood and tissue concentrations increased with exposure time and increasing concentration. See Table 4. Blood and tissue concentrations of HCFC-123 after a 5-min exposure to 1% HCFC-123 (the no-effect level) can be assumed to be the con-

centrations at which there would be no cardiac arrhythmias. Blood and heart-tissue concentrations are considered to be most relevant to the end point of cardiac sensitization. This table shows that Haber's law is not appropriate for this situation because, according to Haber's law, 1% HCFC-123 for 5 min should be equivalent to 5% HCFC-123 for 1 min. The results of this study were that the blood concentration of 5% HCFC-123 for 1 min was approximately 2.5 times greater than that of 1% HCFC-123 for 5 min, and the heart-tissue concentration of 5% HCFC-123 for 1 min was approximately 6 times greater than that of 1% HCFC-123 for 5 min.