Penicillin VK, a widely used antibiotic for treatment of gram-positive coccal infections, was nominated for study by the National Cancer Institute because rodent carcinogenicity studies for this drug had not been performed. The chemical (94% or 98% pure, USP grade) was administered orally (by gavage in corn oil) because oral administration is the primary route used to treat infections in humans. Fourteen-day, 13-week, and 2-year studies were conducted in F344/N rats and B6C3F1 mice. Additional studies were performed to evaluate the potential for genetic damage in bacteria and mammalian cells.
Fourteen-day and thirteen-week studies
In the 14-day studies, penicillin VK was administered at doses of 150-2,400 mg/kg. No compound-related deaths or dose-related histopathologic lesions were seen in rats or mice. Final mean body weights of dosed male rats were 5%-17% lower than that of controls; weights of dosed and control female rats were comparable. Final mean body weights of dosed mice were 5%-9% lower than those of controls. Diarrhea was observed in all dosed groups of rats and mice.
In the 13-week studies, male and female rats received doses of 180-3,000 mg/kg and male and female mice received doses of 250-3,000 mg/kg. No compound-related deaths were seen in rats or mice. Final mean body weights of rats that received 3,000 mg/kg were 11% lower than those of the vehicle controls for males and 6% lower for females. For mice, mean body weights were comparable. Diarrhea occurred in male rats at doses of 750 mg/kg and above and in female rats at doses of 1,500 and 3,000 mg/kg. Mucous cell metaplasia of the glandular stomach was observed in male and female rats receiving 1,500 and 3,000 mg/kg. Lesions of the glandular stomach (inflammation, mucous cell metaplasia, and eosinophilic cytoplasmic change) and the forestomach (papillary hyperplasia and hyperkeratosis) were seen in all groups of dosed mice. The severity of lesions at 1,000 mg/kg or below was considered minimal. Based on these results, doses selected for rats and mice in the 2-year studies were 0, 500, or 1,000 mg/kg.
Two-year studies
Body weight and survival
Mean body weights of dosed and vehicle control male and female rats and male mice were comparable. Mean body weights of dosed female mice were 4%-16% lower than those of the vehicle controls from week 28 to the end of the study. Diarrhea was observed for dosed male and female rats and for dosed male mice. Survival of low and high dose male rats and high dose female rats was reduced (male rats: vehicle control, 34/50; low dose, 19/50; high dose, 16/50;female rats: 29/50; 26/50; 16/50). Survival of male and female mice was comparable to that of the vehicle controls (male mice: 24/50; 36/50; 26/50; female mice: 36/50; 32/50; 32/50).
Nonneoplastic and neoplastic effects
Nonneoplastic lesions occurred at low incidences in the nasal mucosa, lung, and forestomach of dosed male rats and in the nasal mucosa and lung of dosed female rats. Congestion and aspiration pneumonia occurring in dosed rats dying before week 104 was the principal cause of death in these animals.
Nonneoplastic lesions of the gastric fundal gland (eosinophilic cytoplasmic change and dilatation) and glandular stomach (cyst, chronic focal inflammation, hyperplasia, fibrosis, and squamous metaplasia) were seen in dosed male and female mice, and lesions of the gallbladder (eosinophilic cytoplasmic change) were seen in male mice.
Slight increases in the incidences of adenomas of the pituitary gland in high dose male rats and of fibroadenomas or adenomas (combined) of the mammary gland in low dose female rats were observed. These were not considered to be compound-related lesions.
The incidence of hepatocellular adenomas was decreased in high dose male mice (14/50; 15/49; 4/49). No compound-related neoplasms were seen in female mice.
Genetic toxicology
Penicillin VK was not mutagenic in Salmonella typhimurium strains TA98, TA100, TA1535, or TA1537 with or without exogenous metabolic activation. The chemical was mutagenic only with activation in the mouse lymphoma L5178Y/TK+/- forward mutation assay. Incubation of Chinese hamster ovary cells with penicillin VK resulted in increased frequencies of sister chromatid exchanges and chromosomal aberrations in the absence of metabolic activation under the conditions of delayed harvest to compensate for chemical-induced cell cycle delay, no effects from penicillin VK exposure were observed in these cells in the presence of S9.
Data audit
The data, documents, and pathology materials from the 2-year studies of penicillin VK were audited. The audit findings show that the conduct of the studies is documented and support the data and results given in this Technical Report.
Conclusions
Under the conditions of these 2-year gavage studies, there was no evidence of carcinogenic activity of penicillin VK for F344/N rats or for B6C3F1 mice administered 500 or 1,000 mg/kg penicillin VK in corn oil gavage, 5 days per week for 2 years. Nonneoplastic lesions were seen in the glandular stomach of dosed mice. Decreased survival of low and high dose male rats and of high dose female rats reduced the sensitivity of the studies for determining the presence or absence of a carcinogenic response in this species.