William J. Brock

Acute and subchronic toxicity of 1,1-dichloro-1-fluoroethane (HCFC-141b).

The acute and subchronic toxicity of 1,1-dichloro-1-fluoroethane (HCFC-141b), a CFC alternative, was evaluated in several acute and subchronic studies to assist in establishing proper handling guides. Data from acute toxicity studies in rats and rabbits demonstrated that HCFC-141b has very low acute toxicity. HCFC-141b was not a skin irritant, but was a mild eye irritant, in rabbits and was not a skin sensitizer in guinea pigs. Skin application of HCFC-141b to rabbits at 2000 mg/kg body weight produced no adverse effects. Oral administration at 5000 mg/kg body weight did not cause any deaths or clinical signs of toxicity in rats. The 4-hr LC50 for HCFC-141b was about 62,000 ppm in rats. Repeated exposures of rats for 6 hr/day, 5 days/wk for up to 90 days at concentrations of 2000, 8000 or 20,000 ppm did not result in significant adverse effects. Minor, but dose-dependent, reductions in body weight were observed in male and female rats during the 90-day study. Decreased responsiveness was also observed in rats but only at 20,000 ppm. An increase in serum cholesterol or triglycerides was observed in male and female rats at 20,000 ppm, and in males at 8000 ppm. No specific organ pathology was noted in these subchronic inhalation studies. The no-observable-adverse-effect level (NOAEL) from these studies was 8000 ppm. Results from other studies demonstrate that HCFC-141b was not neurotoxic in rats. As with trichlorofluoroethane (CFC-11), a cardiac sensitization response to an intravenous epinephrine challenge occurred in dogs with HCFC-141b at 5000 ppm and higher concentrations in experimental screening studies.

Oral Repeat Dose and Reproductive Toxicity of the Chlorinated Flame Retardant Dechlorane Plus

This study consisted of a 28-day oral repeat dose (repeat dose toxicity [RDT]) phase and a developmental and reproductive (developmental and reproductive toxicity [DART]) phase with rats. Rats were treated with Dechlorane Plus at doses of 0, 750, 1500, or 5000 mg/kg by gavage. For the RDT phase, no effects were observed on in-life parameters or clinical or anatomic pathology. In the DART phase, no effects were observed on reproductive or fertility indices, or fetal development through lactation day (LD) 4. No effects were noted on gestation day (GD) 20 implantation data, fetal indices, or external and visceral examinations. Mortalities occurred across all dose groups, although these were gavage-related errors and not compound related. Microscopic evidence of gavage-related errors included adhesions, inflammation, and fibrosis in the thoracic and pleural cavities. These findings were not test article related as they were observed only in animals with evidence of gavage injury. The no-observable-effect level (NOEL) in both phases of study was 5000 mg/kg.

Acute, Subchronic, and Developmental Toxicity and Genotoxicity of 1,1,1-Trifluoroethane (HFC-143a)

The toxicity potential of 1,1,1-trifluoroethane (HFC-143a), a CFC alternative, was evaluated in several acute, subchronic, and developmental toxicity studies by the inhalation route and in genotoxicity studies. HFC-143a has a very low acute inhalation toxicity potential as shown by a 4-hr LC50 of > 540,000 ppm in rats. HFC-143A has a low potential to induce cardiac sensitization in experimental screening studies in dogs; only the highest concentration tested--300,000 ppm--elicited a cardiac sensitization response. In an initial 4-week nose-only inhalation study, male and female rats were exposed 6 hr/day, 5 days/week at concentrations of 0, 2000, 10,000, or 40,000 ppm. Females showed no evidence of toxicity at any exposure level; male rats did exhibit degenerative changes only in the tests at all exposure levels. However, because of exposure system irregularities, which resulted in excessive temperature conditions and stress in the HFC-143a-exposed groups, the study was repeated in male rats exposed by whole-body inhalation. In this repeat study no toxicity was observed at < or = 40,000 ppm. Moreover, a subsequent 90-day whole-body inhalation study in rats exposed 6 hr/day, 5 days/week at 0, 2000, 10,000, or 40,000 ppm resulted in no evidence of toxicity at any exposure concentration. The results of the second 4-week and the 90-day studies using whole-body exposures indicate that the findings from the first 4-week study were related to the stress induced by excessive temperatures and nose-only restraint. Therefore, the no-observed-effect level (NOEL) for rats repeatedly exposed up to 90 days was considered to be 40,000 ppm. In developmental toxicity studies with rats and rabbits, an increase in visceral variations or skeletal malformations was observed, respectively, at HFC-143a concentrations of 2000, 10,000 or 40,000 ppm (rat) or at the low and high concentrations (rabbit). Because of the unusually low control incidence of variations (1.6% per litter in the control versus 6.8-16.8% for historical control values), the lack of a clear dose-response relationship, and the lack of other developmental effects, these findings were not considered related to HFC-143a exposure. In addition, results from genotoxicity studies (Ames, chromosomal aberration with human lymphocytes, mouse micronucleus) demonstrated that HFC-143a was not mutagenic.

Assignment of Skin Notation for Threshold Limit Values Chemicals Based on Acute Dermal Toxicity

Abstract The skin notation with a threshold limit value (TLV) indicates that significant quantities of the chemical may be absorbed through that route to produce unwanted systemic effects. The relationship between the dermal LD50 for a given chemical and the occurrence of skin irritation in the TLV was examined. An association was found, but it was weak. We suggest that all chemicals found to have LD50 values lower than 1000 mg/kg be initially assigned a skin notation until more definitive work proves otherwise. Further, effects that can be produced following repeated dermal exposures using reasonable dose concentrations need to be evaluated for the purpose of a skin notation. Extrapolation of dermal effects following information from other routes of administration needs to be carefully considered, particularly when the absorption and distribution of the chemical following various routes (including dermal) are known. Kennedy, G.L., Jr.; Brock, W.J.; Banerjee, A.K.: Assignment of Skin Notation for Threshol...

Hepatic macromolecular binding and tissue distribution of ortho- and para-toluidine in rats

The in vivo covalent binding of ortho- and para-toluidine (OT and PT) to rat hepatic macromolecules was investigated to determine if a relationship exists between the degree of binding for each isomer and its carcinogenic potency. The ortho-isomer has been shown to be a more potent hepatocarcinogen than the para-isomer. In addition to the macromolecular binding, the tissue distribution of each isomer was also measured. The degree of binding to hepatic macromolecules appeared to be at maximum for both at 24 28 h following dosing. At 24 h following dosing, the level of DNA binding of OT was approximately 1.2-fold lower than that of PT. The binding to RNA and protein was also lower for OT than PT, although the differences were not as great as that observed for DNA binding. There were subtle differences in tissue distribution for each isomer. However, in contrast to the macromolecular binding data, the area under the plasma concentration curve for OT was approximately 1.8-fold greater than that for PT. Based on the results of these studies, there was no direct correlation between the degree of macromolecular binding and carcinogenic potency.

Ocular Toxicity Assessment From Systemically Administered Xenobiotics Considerations in Drug Development

The eye is a unique sensory structure, which must be evaluated for toxicity to determine the safety of drugs, industrial chemicals, and consumer products. Changes in the structure and/or function of ocular tissues following systemic administration of a potential new drug in preclinical animal models can result in significant delays in the development of a new therapeutic and in some cases lead to termination of the development. The ability to detect and characterize ocular toxicity in preclinical models and to predict risk in patients is critically dependent on the preclinical testing strategy, the availability and use of state-of-the-art ocular safety assessment tools, and the knowledge of drug mechanism of action and the current regulatory environment. This review describes the design and execution of toxicity studies with the incorporation of current methods for in vivo assessment of ocular toxicity, including methods for detecting early changes in the eye. In addition, anatomical differences among laboratory animals, preparation of globes for examination, and iatrogenic and spontaneous ocular findings are described that can affect interpretation of toxicological findings. Finally, the correlation between nonclinical outcomes and clinical evaluations is discussed in terms of expected therapeutic uses, indications, and regulatory consequences of ocular effects.

Inhalation Toxicity and Genotoxicity of Hydrofluorocarbon (HFC)-236fa and HFC-236ea

The acute, subchronic, and developmental and genetic toxicity of hydrofluorocarbon (HFC)-236fa and HFC-236ea were evaluated to assist in establishing proper handling guidance. In acute inhalation studies, rats were exposed whole body for 4 hours to various concentrations of each isomer. Based on the lack of mortality, the approximate lethal concentration for HFC-236ea for male rats was > 85,000 ppm. For HFC-236fa, the LC50 for males and females (combined) was > 457,000 ppm. Narcotic-like effects, e.g., prostration, incoordination, and reduced motor activity, were observed only during exposure to either isomer, but were not evident after termination of exposure. In cardiac sensitization studies, HFC-236ea induced cardiac sensitization at ≥ 35,000 ppm, with fatal responses occurring at 50,000 ppm and greater. For HFC-236fa, a cardiac sensitization response was observed at 150,000 ppm and greater but not at 100,000 ppm. A fatal cardiac sensitization response was observed in one dog exposed to 150,000 ppm HFC-236fa. In 90-day subchronic inhalation studies, male and female rats were exposed whole body to HFC-236ea at concentrations of 0, 5000, 20,000, or 50,000 ppm for 6 hours/day, 5 days/week. Similarly, male and female rats were exposed whole body to HFC-236fa at concentrations of 0, 5000, 20,000, or 50,000 ppm for 6 hours/day, 5 days/week. During exposure, narcotic-like effect (reduced acoustic startle response) was observed at 50,000 ppm with both isomers, although there appeared to be an adaptive response to this effect as the study progressed. With HFC-236ea, dilatation of the seminiferous tubules, without effects on germ or Sertoli cells, was observed only in rats at 50,000 ppm. No other effects on in-life measures or on clinical or anatomic pathology, including histopathology, were observed for either isomer. In rat developmental toxicity studies, no evidence of embryotoxicity or teratogenicity was observed with either isomer exposed up to 50,000 ppm during gestational days 7 to 16. Also, no developmental toxicity was observed in rabbits exposed to HFC-236fa at concentrations of up to 50,000 ppm during gestational days 7 to 19. Neither of the HFC-236 isomers was mutagenic in the Ames reverse mutation assay or clastogenic in the chromosomal aberration assay with human lymphocytes. No increase in chromosomal aberrations was observed in in vivo micronucleus studies with either isomer.

Nonclinical Safety Assessment: A Guide to International Pharmaceutical Regulations

Description: Bringing a new drug to market is a costly time–consuming process. Increased regional and international regulation over the last twenty years, while necessary, has only served to amplify these costs. In response to this escalation, developmental strategies have shifted towards a more global approach. In order to create the most cost–effective and safe processes, it is critical for those bringing drugs to market to understand both the globally accepted regulations and the local variations. Nonclinical Safety Assessment: A Guide to International Pharmaceutical Regulations provides a practical description of nonclinical drug development regulations and requirements in the major market regions.

The In Vitro and In Vivo Genotoxicity of Benzocaine: A Brief Communication:

Benzocaine has a long history of use in human medicine. However, benzocaine also has been used in aquaculture with finfish for more than 40 years for sedating fish for marking, transport, surgery, and so on, although benzocaine does not have a current Food and Drug Administration (FDA) approval for this application in the United States. As part of a FDA approval for use as an animal drug, the genotoxicity of benzocaine was evaluated in the in vitro bacterial reverse mutation assay and the forward mutation assay and in vivo in the mouse micronucleus assay. These studies were conducted in compliance with Good Laboratory Practice regulations and according to Veterinary International Conference on Harmonisation guidelines. Based on the results of these studies, benzocaine was determined not to be genotoxic.

Chronic Toxicity, Oncogenicity, and Mutagenicity Studies with Chlorotetrafluoroethane (HCFC-124)

The chronic toxicity, oncogenicity, and mutagenicity of chlorotetrafluoroethane (HCFC-124) were evaluated. In the chronic toxicity/oncogenicity study, male and female rats were exposed to 0, 2000, 10,000, or 50,000 ppm HCFC-124 for 6 hr/day, 5 days/week, for 2 years. Body weights were obtained weekly during the first three months of the study and every other week for the remainder of the study. Food consumption was determined weekly. Clinical signs of toxicity were monitored throughout the study. An ophthalmological examination was performed on all animals prior to study start, and all surviving rats were examined at approximately 3, 12, and 24 months after study start. Clinical pathology was evaluated at 3, 6, 12, 18, and 24 months. An interim termination was conducted at 12 months. All surviving rats were necropsied at 24 months. A complete set of tissues was collected for microscopic examination, and selected tissues were weighed. There were no compound-related, adverse effects on body weight, food consumption, survival, clinical signs of toxicity, ophthalmoscopically observable ocular lesions, serum hormone concentrations, or clinical pathology parameters at any exposure concentration in either male or female rats. Compared to controls, urine fluoride was increased in males and females at all exposure concentrations, and plasma fluoride was increased in females at all exposure concentrations. Excretion of fluoride represents conversion of the parent molecule, and as such is not considered to be an adverse effect. There were no toxicologically significant, compound-related organ weight changes or gross or microscopic findings in male or female rats at any of the exposure concentrations tested. HCFC-124 was not toxic or carcinogenic in rats of either sex after inhalation exposure at concentrations of up to 50,000 ppm in this two-year chronic toxicity/oncogenicity study. After exposure to HCFC-124 for six hours per day, five days per week, for 24 months, the no-observed-adverse-effect level for male and female rats was 50,000 ppm. HCFC-124 was not mutagenic in Salmonella typhimurium strains TA1535, TA97, TA98, and TA100 with and without activation when evaluated at concentrations up to 60% HCFC-124 for 48 hours. No evidence of clastogenic activity was observed in cultured human lymphocytes at atmospheric concentrations up to 100% HCFC-124 for 3 hours, with and without metabolic activation. In vivo, no micronuclei were induced in mouse bone marrow cells following exposure of mice to concentrations of 99,000 ppm HCFC-124 6 hours/day for 2 days.