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Am J Obstet Gynecol. 2002 Jan;186(1):100-2.

Acyclovir concentrations in human breast milk after valaciclovir administration.

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Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center at Dallas, 75390-9032, USA.



The purpose of this study was to determine the valaciclovir and acyclovir pharmacokinetic profiles in serum and breast milk after valaciclovir administration to women after delivery.


Valaciclovir (500 mg twice daily for 7 days) was given to 5 women after delivery who were breast-feeding healthy term infants. Matched serum and breast milk samples were obtained after the initial dose, on day 5 and 24 hours after the drug was discontinued. Infant urine was obtained on day 5.


Valaciclovir was rapidly converted to acyclovir. The peak serum acyclovir concentration occurred 3 hours before the peak breast milk concentration (2.7 microg/mL at 1 hour vs 4.2 microg/mL at 4 hours). The serum acyclovir elimination half-life was 2.3 hours. The ratio of breast milk to serum acyclovir concentration was highest 4 hours after the initial dose at 3.4 and reached steady state ratio at 1.85. The median infant urine acyclovir concentration at steady state was 0.74 microg/mL.


Valaciclovir is rapidly converted to acyclovir and concentrates in breast milk. However, the amount of acyclovir in breast milk after valaciclovir administration is considerably less (2%) than that used in therapeutic dosing of neonates.

[Indexed for MEDLINE]

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