Can I take aciclovir while pregnant or breastfeeding?

Pregnancy Teratogenic Effects: Pregnancy Category B. Acyclovir administered during organogenesis was not teratogenic in the mouse (450 mg/kg/day, p.o.), rabbit (50 mg/kg/day, s.c. and IV), or rat (50 mg/kg/day, s.c.). These exposures resulted in plasma levels 9 and 18, 16 and 106, and 11 and 22 times, respectively, human levels. There are no adequate and well-controlled studies in pregnant women. A prospective epidemiologic registry of acyclovir use during pregnancy was established in 1984 and completed in April 1999. There were 749 pregnancies followed in women exposed to systemic acyclovir during the first trimester of pregnancy resulting in 756 outcomes. The occurrence rate of birth defects approximates that found in the general population. However, the small size of the registry is insufficient to evaluate the risk for less common defects or to permit reliable or definitive conclusions regarding the safety of acyclovir in pregnant women and their developing fetuses. Acyclovir should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Prescribing label, section “Pregnancy”: Acyclovir (oral), NuCare Pharmaceuticals, Inc. Label on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.

Even with the highest maternal dosages, the dosage of acyclovir in milk is only about 1% of a typical infant dosage and would not be expected to cause any adverse effects in breastfed infants.[1] Acyclovir is considered a treatment of choice for Herpes infections during breastfeeding.[2] Topical acyclovir applied to small areas of the mother's body away from the breast should pose no risk to the infant. Only water-miscible cream or gel products should be applied to the breast because ointments may expose the infant to high levels of mineral paraffins via licking.[3]

“Summary of Use during Lactation”, LactMed record “Acyclovir” (LM331), quoted verbatim. Everything LactMed reports about Acyclovir while breastfeeding.

Nursing Mothers Acyclovir concentrations have been documented in breast milk in 2 women following oral administration of acyclovir tablets and ranged from 0.6 to 4.1 times corresponding plasma levels. These concentrations would potentially expose the nursing infant to a dose of acyclovir up to 0.3 mg/kg/day. Acyclovir tablets should be administered to a nursing mother with caution and only when indicated.

Prescribing label, section “Nursing Mothers”: Acyclovir (oral), NuCare Pharmaceuticals, Inc. Label on DailyMed. Quoted verbatim; US labels are written for US prescribers and patients.