The drug valaciclovir is a prodrug of acyclovir, which is quickly transformed after the patient takes.
Given that the highest dose of valacyclovir that may ingest an infant is much lower than the therapeutic doses administered to these young patients, it is unlikely to cause adverse effects on the baby. Some studies suggest that the total dose received by a baby with exclusive breastfeeding could reach 0.34 mg/kg/day, about one hundred times lower than the therapeutic dose of the infant.
Warning of the manufacturer:
Acyclovir, the major metabolite of valaciclovir, is excreted in breast milk. Following oral administration of 500 mg of valaciclovir, acyclovir maximum concentrations (Cmax) in breast milk ranged from 0.5 to 2.3 (mean 1.4) times the values for maternal serum concentrations of acyclovir. The relationship between the AUC of acyclovir in breast milk and maternal serum ranged from 1.4 to 2.6 (median 2.2). The average concentration of acyclovir in the breast milk was 2.24 mcg / ml. With a valaciclovir dosage of 500 mg twice daily, the infant could be exposed to a daily oral acyclovir dose of about 0.61 mg/kg/day. The elimination half-life of acyclovir in breast milk is similar to that of plasma.
Valacyclovir was not detected unchanged in the maternal serum, breast milk or infant urine.
Care should be taken when administered valacyclovir to lactating women. However, acyclovir is used for treating herpes simplex neonatal at intravenous doses of 30 mg/kg/day.