The effect of ornidazole on fertility and epididymal sperm function in rats.

A comprehensive study of male fertility and sperm production and function was performed in 20 control and 20 rats treated with ornidazole, a compound with trichomonacidal activity. Rats were treated for 4 weeks at dosages of 0 (control) and 400 mg/kg/day of ornidazole during which fertility was assessed by weekly matings. Testicular sperm production and epididymal sperm function were assessed in one-half of the rats while the reversibility of effects after a 2-week recovery period was assessed in the remaining half. Male rats treated with ornidazole were infertile during the second week of treatment. After 4 weeks of treatment, testicular and epididymal weights, testicular spermatid counts, epididymal sperm reserves, sperm morphology, and sperm viability were similar in treated and control rats. A quantitative assessment of epididymal sperm motility using a dark-field photomicroscope with a stroboscopic light source revealed that ornidazole markedly inhibited sperm motility. Although the percentage of nonmotile sperm was not substantially increased in treated rats, the vigor of tail movement was markedly decreased which resulted in decreased sperm velocity. Restoration of fertility and normal sperm motility and velocity were observed in the group of recovery rats assessed 2 weeks after the cessation of ornidazole treatment. It is concluded that ornidazole, at a high dosage of 400 mg/kg/day, produces infertility in male rats by inhibiting epididymal sperm motility in terms of decreased sperm velocity. These effects are rapidly reversible after the cessation of treatment.