Reproduction studies in rats treated with ornidazole

Reproduction studies were performed with ornidazole, a compound with trichomonacidal activity. Male rats were treated for 61 days prior to mating and female rats were treated for 2 weeks prior to mating and throughout gestation and lactation at doses of 0 (control), 25, 100, and 400 mg of ornidazole/kg/day. A decrease in the pregnancy rate was observed in high-dose rats without altered mating performance. Crossover matings between high-dose treated and control male and female rats showed that male but not female fertility was affected and that the effect on fertility was reversible within several days after the cessation of treatment. Testicular and epididymal weights were not altered in treated male rats. Histopathological examination revealed that spermatogenesis and the testes were normal and that the epididymides of treated male rats contained normal appearing sperm. It is concluded that ornidazole, at high dosages, produces infertility in the male rat; however, unlike many other 5-nitroimidazole compounds which are reported to inhibit spermatogenesis, no effect on spermatogenesis was observed under the conditions of these studies. This in conjunction with the rapid reversibility of infertility suggests that the mode of action of ornidazole involves a rapidly reversible effect on epididymal sperm function.