Toxicity and Carcinogenicity Studies of Oxazepam in the Fischer 344 Rat

Oxazepam and related benzodiazepines are used in the treatment of anxiety. Carcinogenicity studies of oxazepam were performed with the F344 rat because of marked differences in tumor responses observed in NTP studies with B6C3F1 and Swiss-Webster mice compared to the results of Sprague-Dawley rat studies submitted to the FDA by a manufacturer to support registration of the drug. Groups of 50 male and 50 female F344/N rats were fed diets containing 0, 625, 2500, or 5000 ppm oxazepam for up to 105 weeks. A stop-exposure group of 50 males and 50 females received 10,000 ppm oxazepam in diet for 26 weeks, after which animals received control diet. All 5000- and 10, 000-ppm stop-exposure males died before the end of the study. Survival of 2500-ppm males and females was lower than that of controls. Body weight gains of 2500- and 5000-ppm males and females were less than those of controls. Male rats exposed to 2500 ppm had an increased incidence of renal tubule adenoma and hyperplasia. In addition, the incidences of renal tubule adenoma and hyperplasia were increased in the 10,000-ppm stop-exposure group. The incidences of nephropathy in exposed females were greater than those in controls, and the severity of nephropathy increased in exposed males. Epithelial hyperplasia and chronic inflammation of the nonglandular stomach were increased in males given 2500 and 5000 ppm and the incidence of ulcers of the nonglandular stomach in 2500-ppm males was also greater than that in controls. In males exposed to 5000 ppm, mineralization of the glandular stomach and erosion of the duodenum were observed. In females exposed to 2500 ppm, the incidences of epithelial hyperplasia, chronic inflammation, and ulcers of the nonglandular stomach and the incidence of erosion in the glandular stomach were increased. The incidences of centrilobular hepatocyte hypertrophy in males and females given 2500 and 5000 ppm were greater than those in controls. In summary, there was equivocal evidence of carcinogenicity in males based on increased renal tubule adenomas in groups which also had significantly enhanced nephropathy. There was no evidence of carcinogenicity of oxazepam in females given a diet containing 625, 2500, or 5000 ppm for 2 years or 10,000 ppm for 6 months.