Can a breastfeeding mother safely take valacyclovir for genital herpes or varicella‑zoster without interrupting nursing?

Valacyclovir Safety in Breastfeeding

Breastfeeding mothers can safely take valacyclovir for genital herpes or varicella-zoster without interrupting nursing. 1

Evidence from FDA Drug Labeling

The FDA label for valacyclovir provides direct safety data for nursing mothers. Following a 500 mg dose of valacyclovir twice daily, acyclovir (the active metabolite) concentrations in breast milk ranged from 0.5 to 2.3 times maternal serum levels (median 1.4), with breast milk AUC ranging from 1.4 to 2.6 times maternal serum AUC (median 2.2). 1

Critically, a nursing infant would receive approximately 0.6 mg/kg/day of acyclovir through breast milk—less than 2% of the standard therapeutic neonatal intravenous dose of 30 mg/kg/day. 1 This exposure is clinically insignificant and well below any therapeutic threshold. 1

Unchanged valacyclovir was not detected in maternal serum, breast milk, or infant urine, confirming rapid conversion to acyclovir. 1

Supporting Clinical Research

Pharmacokinetic Studies

A 2002 study of five breastfeeding women receiving valacyclovir 500 mg twice daily for 7 days demonstrated that peak breast milk acyclovir concentrations (4.2 mcg/mL at 4 hours) occurred 3 hours after peak serum levels (2.7 mcg/mL at 1 hour). 2 The breast milk-to-serum ratio reached steady state at 1.85, and median infant urine acyclovir concentration was only 0.74 mcg/mL. 2 The authors concluded that acyclovir exposure through breast milk represents only 2% of therapeutic neonatal dosing. 2

An earlier 1994 case report of a woman receiving high-dose acyclovir 800 mg five times daily for herpes zoster (equivalent to much higher exposure than typical valacyclovir dosing) found breast milk concentrations of 4.16–5.81 mcg/mL, resulting in an estimated infant dose of 0.73 mg/kg/day—approximately 1% of the maternal dose per kilogram. 3 The infant was nursed without adverse effects. 3

Safety in Context of Antiretroviral Therapy

A 2012 randomized trial of 148 HIV-1/HSV-2 co-infected pregnant women receiving valacyclovir 500 mg twice daily from 34 weeks gestation through 12 months postpartum (in conjunction with zidovudine and nevirapine for PMTCT) demonstrated no infant or maternal toxicities or adverse events. 4 Acyclovir was detected in 80% of breast milk samples at 2 weeks postpartum (median 2.62 mg/mL, maximum 10.15 mg/mL), yet all infant creatinine levels were normal and infant growth did not differ between study arms. 4 This provides reassurance even with prolonged maternal valacyclovir exposure combined with antiretroviral drugs. 4

Clinical Recommendations

For Genital Herpes Treatment

• First episode: Valacyclovir 1 g orally twice daily for 7–10 days is appropriate during breastfeeding. 5, 6
• Recurrent episodes: Standard episodic or suppressive therapy regimens are compatible with nursing. 5, 7
• The FDA label advises that "caution should be exercised" when administering valacyclovir to nursing women, but this is standard regulatory language; the actual safety data strongly support continued breastfeeding. 1

For Varicella-Zoster (Shingles) Treatment

• Uncomplicated herpes zoster: Valacyclovir 1 g orally three times daily for 7 days (or until all lesions have scabbed) is safe during breastfeeding. 8, 9
• Severe or disseminated disease: If intravenous acyclovir is required (10 mg/kg every 8 hours), breastfeeding can continue as infant exposure remains minimal. 8

For Varicella (Chickenpox) in Pregnancy/Postpartum

• Acyclovir 800 mg five times daily initiated within 24 hours of rash onset is recommended for pregnant women at risk of moderate-to-severe varicella, and breastfeeding can continue postpartum. 10
• Varicella-zoster immune globulin (VZIG) should be administered within 96 hours to seronegative pregnant women exposed to varicella, but this does not contraindicate subsequent breastfeeding if valacyclovir is needed. 10

Key Counseling Points

No interruption of breastfeeding is necessary. The infant receives less than 2% of a therapeutic neonatal dose through breast milk, which is pharmacologically insignificant. 1, 2

Monitor the infant for normal feeding, growth, and development, though adverse effects are not expected based on the low exposure levels. 1

Maternal hydration should be maintained during valacyclovir therapy to minimize nephrotoxicity risk, though this is a maternal rather than infant concern. 8

Common Pitfalls to Avoid

• Do not advise "pumping and dumping"—this is unnecessary given the minimal infant exposure and lack of safety concerns. 1, 2
• Do not delay treatment due to breastfeeding concerns, as untreated maternal herpes infections pose greater risks than the negligible drug exposure through breast milk. 6, 1
• Do not confuse valacyclovir safety with other antivirals—the extensive safety data are specific to valacyclovir/acyclovir and should not be extrapolated to other agents without similar evidence. 1