ObjectiveTo determine the effect of udenafi l, a cyclic monophosphate-specifi c type 5 phosphodiesterase inhibitor, on fertilization and early embryo cleavage of mice. MethodsThis mammal study included randomly assigned male and female mice. The females were sacrifi ced after mating to evaluate their oocytes and embryos in four different time intervals following the treatment. Female mice were injected intraperitoneally with 5 IU of gonadotropin and human chorionic gonadotropin to stimulate follicular growth and induce ovulation. They were separately caged with males that had been gavaged with udenafi l (0.06 mg/0.05 mL) and allowed to mate. After 24, 48, 72, and 96 hours of time intervals, females were killed, their oviducts were dissected out, and retrieved embryos were assessed for blastomere number and quality. Fertilization rates and numbers of embryos were evaluated after treatment. ResultsFertilization rates were reduced in females that were mated with udenafi l gavaged males. Over days 2-4, the numbers of embryo that of the treated group were signifi cantly fewer than in the control group. There was also a tendency of impaired cleavage rates with those embryos. ConclusionThe impairments of fertility caused by udenafi l have important implications for infertility centers and couples who are using this drug precoitally while attempting to conceive.