Acyclovir Pregnancy and Breastfeeding Warnings

Acyclovir is also known as: Zovirax

Acyclovir Pregnancy Warnings

Studies to determine the pharmacokinetics and tolerability of acyclovir given near term have reported maternal-cord ratios of 0.6 to 1.9 at delivery. The pharmacokinetics of acyclovir are not significantly affected by pregnancy. No toxicity has been reported in mother or neonates. The Acyclovir in Pregnancy Registry was established in 1984 by the manufacturer and the Centers for Disease Control and Prevention (CDC) and completed in April 1999. The incidence of adverse events reported, in the 749 pregnancies followed in women exposed to systemic acyclovir during the first trimester of pregnancy resulting in 756 outcomes, approximates that of the general population. Given the small size of the registry there are no sufficient data to assess the safety of acyclovir in pregnant women and the fetus. Women exposed to systemic acyclovir during pregnancy may contact the Registry by calling GlaxoSmithKline, Inc., at (888) 825-5249. In the U.S. Michigan Medicaid study involving surveillance of 229,101 pregnancies from 1985 to 1992, there were 478 first trimester exposures to systemic acyclovir. Eighteen major birth defects were reported (versus 20 expected), including cardiovascular defects, polydactyly, limb reduction, and hypospadia. There was no evidence of an association between first trimester use of acyclovir and major groups of malformations. Acyclovir use has also been studied in five patients prior to delivery to determine the effects on asymptomatic shedding of the virus and vertical transmission to the neonate. Asymptomatic shedding and viral transmission to the infant occurred in one case. The CDC recommend the use of intravenous acyclovir in pregnant patients for the treatment of life-threatening herpes infections, including encephalitis, pneumonitis and hepatitis. Acyclovir has also been recommended for the treatment of severe or progressive maternal varicella infection. However, the use of acyclovir during pregnancy for non-life-threatening infections or for suppressive therapy is not recommended by the CDC. Primary herpes simplex infection during pregnancy has been treated with acyclovir, although this practice remains controversial. Some have suggested that acyclovir decreases the incidence of adverse pregnancy outcomes such as prematurity and growth retardation.

Acyclovir has been assigned to pregnancy category B by the FDA. Nonstandard animal studies have produced fetal abnormalities, while standard animal testing failed to reveal evidence of teratogenicity. There are no controlled data in human pregnancy. Acyclovir is only recommended for use during pregnancy when benefit outweighs risk.

Acyclovir Breastfeeding Warnings

In one woman, measurement of breast milk levels revealed her infant was exposed to 1% of the maternal dosage, or 0.73 mg/kg/day. No adverse effects were noted in this breast-feeding infant.

Acyclovir is excreted into and concentrated in human milk. Adverse effects in breast-feeding infants associated with exposure to acyclovir via breast milk have not been reported in the literature. Acyclovir is considered compatible with breast-feeding by the American Academy of Pediatrics. Moreover, acyclovir is used to treat viral infections in neonates.

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