Nalidixic acid is an antimicrobial agent to treat bacterial infections of the urinary tract. Toxicology and carcinogenesis studies were conducted by feeding diets containing nalidixic acid (approximately 99% pure) to groups of F344/N rats and B6C3F1 mice of each sex for 13 weeks or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, mouse lymphoma cells, and Chinese hamster ovary (CHO) cells.
Thirteen-week studies
Nalidixic acid was administered at dietary concentrations ranging from 1,000 to 16,000 ppm. One female rat that received 16,000 ppm nalidixic acid died before the end of the studies; no other compound-related deaths occurred in rats and mice. The final mean body weights of rats that received 8,000 or 16,000 ppm were 23% or 49% lower than those of controls for males and 11% or 31% lower for females. Feed consumption by rats receiving 16,000 ppm was approximately two-thirds that by controls. Liver weight to body weight ratios for male rats that received 2,000 ppm or more and female rats that received 8,000 ppm or more were significantly greater than those for controls. Degeneration of the germinal epithelium in the seminiferous tubules of the testis was observed in 10/10 male rats that received 16,000 ppm; no other compound-related histopathologic effects were observed in rats. The final mean body weights of mice that received 8,000 or 16,000 ppm were 10%-20% lower than those of controls. Feed consumption by dosed mice was similar to that by controls. Liver weight to body weight ratios were significantly greater for male mice receiving 2,000, 8,000, or 16,000 ppm and for female mice receiving 4,000, 8,000, or 16,000 ppm than for the controls. No compound-related histopathologic effects were observed in mice.
Based on these results, 2-year studies of nalidixic acid were conducted by feeding diets containing 0, 2,000, or 4,000 ppm nalidixic acid to groups of 50 male and 50 female F344/N rats and 50 male and 50 female B6C3F1 mice.
Two-year studies
Body weight and survival
Mean body weights of high dose rats were 7%-23% lower than those of controls, and those of low dose male rats were 6%-11% lower than those of controls. The average daily feed consumption by dosed rats ranged from 89% to 96% that by controls. The average amount of nalidixic acid consumed per day was approximately 80 or 175 mg/kg for low dose or high dose rats. Mean body weights of high dose male mice were 1%-8% lower than those of controls throughout the study. Mean body weights of dosed female mice were 5%-17% lower than those of controls. Average daily feed consumption by dosed mice was within 3% of that by controls. The estimated average amount of nalidixic acid consumed per day was approximately 220 or 475 mg/kg for low dose or high dose mice. No significant differences in survival were seen between any groups of rats or mice of either sex after 2 years (male rats: control, 27/50; low dose, 28/50; high dose, 27/50; female rats: 22/50; 31/50; 29/50; male mice: 33/50; 34/50; 31/50; female mice: 40/50; 43/50; 32/50).
Nonneoplastic and neoplastic effects
The incidences of preputial gland neoplasms in dosed male rats and of clitoral gland neoplasms in dosed female rats were significantly greater than those in controls (male--preputial gland adenomas, papillomas, or carcinomas, combined: control, 3/49; low dose, 19/49; high dose, 20/47; female--clitoral gland adenomas, papillomas, or carcinomas, combined: 5/46; 15/46; 16/47).
A squamous cell carcinoma of the tongue was seen in two high dose male rats. The historical incidence of oral cavity neoplasms in untreated control male F344/N rats is 7/1,596 (0.4%).
There were decreased incidences of leukemia (20/50; 9/50; 7/50) and mammary gland neoplasms (10/50; 7/50; 2/50) in dosed female rats and of pituitary gland neoplasms (11/49; 2/50; 2/50) in dosed male rats.
Retinal degeneration and cataracts of the eye were observed at increased incidences in dosed rats (degeneration--male: 4/48; 41/48; 47/49; female: 2/47; 40/48; 46/50; cataracts--male: 11/48; 23/48; 38/49; female: 0/47; 18/48; 14/50). The cause of these cataracts and retinal degeneration is uncertain because cages were not rotated and low and high dose groups of rats may have been exposed to greater light intensity than were the controls.
Subcutanous tissue fibrosarcomas and fibromas or fibrosarcomas (combined) were increased in dosed male mice (fibromas or fibrosarcomas, combined: 5/50; 9/50; 14/50). There were no increased incidences of neoplasms in dosed female mice.
Genetic toxicology
Nalidixic acid was not mutagenic in any of several in vitro short-term tests. No gene reversion was observed in S. typhimurium strains TA97, TA98, TA100, or TA1535 after exposure to nalidixic acid in either the presence or absence of exogenous metabolic activation. Results of tests for induction of trifluorothymidine resistance in mouse L5178Y/TK lymphoma cells were negative with or without metabolic activation. In CHO cells, nalidixic acid did not induce sister chromatid exchanges or chromosomal aberrations in either the presence or absence of activation.
Conclusions
Under the conditions of these 2-year feed studies, there was clear evidence of carcinogenic activity of nalidixic acid for F344/N rats, as indicated by increased incidences of preputial gland neoplasms in males and clitoral gland neoplasms in females. There was equivocal evidence of carcinogenic activity for male B6C3F1 mice fed diets containing nalidixic acid, as indicated by marginally increased incidences of subcutaneous tissue neoplasms. There was no evidence of carcinogenic activity for female B6C3F1 mice fed diets containing 2,000 or 4,000 ppm nalidixic acid for 2 years.