Famciclovir was tested on embryo-fetal development in rats and rabbits at oral doses up to 1000 mg/kg/day; IV doses of 360 mg/kg/day in rats and 120 mg/kg/day in rabbits were also tested. No adverse effects were observed on embryo-fetal development.

To monitor maternal-fetal outcomes of pregnant women exposed to famciclovir a pregnancy registry has been established. Physicians are encouraged to register their patients at 888-669-6682.

Famciclovir has been assigned to pregnancy category B. Animal studies failed to reveal evidence of teratogenicity. There are no controlled data in human pregnancy. Famciclovir should only be given during pregnancy when need has been clearly established.

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There are no data on the excretion of famciclovir into human milk. Following oral administration of famciclovir to lactating rats, its active metabolite penciclovir was excreted in breast milk at concentrations higher than those seen in the plasma. There are no data on the safety of penciclovir in nursing infants. The manufacturer recommends that famciclovir should not be administered to nursing women unless the benefit outweighs the risk. The U.S. Public Health Service Centers for Disease Control and Prevention advise HIV-infected mothers not to breast-feed to avoid postnatal transmission of HIV to a child who may not yet be infected.

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