A Phase 1 study that will determine the valacyclovir dose that results in a systemic acyclovir exposure comparable to 10 mg/kg of parenterally administered acyclovir, which is an AUC0-12 of 24,000 ngxhr/mL to 48,000 ngxhr/mL. Neonates at risk of acquiring neonatal HSV will be enrolled in one of 2 cohorts. Cohort 1 will be comprised of eight subjects who will receive an initial dose of 10ml/kg of oral valacyclovir. Samples for PK assessments will be obtained to assess the exposure concentration. If the safety profile and the drug exposure concentrations in Cohort 1 are acceptable, eight new subjects will be enrolled in Cohort 2. The dose that these subjects will receive will be predicated upon the pharmacokinetic data from Cohort 1.

A Phase 1, open label multicenter trial to assess the safety and pharmacokinetics (PKs) of oral valacyclovir in neonates who are at risk of acquiring neonatal herpes simplex virus disease. This study will determine the valacyclovir dose that results in a systemic acyclovir exposure comparable to 10 mg/kg of parenterally administered acyclovir, which is an AUC0-12 of 24,000 ngxhr/mL to 48,000 ngxhr/mL. Neonates whose mothers have a history of genital HSV infection and received oral valacyclovir in the last several weeks of pregnancy, as per the recommendations of the American College of Obstetrics and Gynecology (ACOG) (9), will be eligible for enrollment. Cohort 1 will be comprised of eight subjects. Following informed consent, each subject will receive 10 mg/kg of oral valacyclovir, and may start taking oral valacyclovir while still in the birth hospital, with subsequent dosing at home, or may start taking oral valacyclovir following discharge from the birth hospital. If the safety profile and the drug exposure concentrations in Cohort 1 are acceptable, eight new subjects will be enrolled in Cohort 2. The dose that these subjects will receive will be predicated upon the pharmacokinetic data from Cohort 1. The primary study objective is to establish the dose of valacyclovir in neonates that reliably achieves systemic acyclovir exposures comparable to 10 mg/kg of parenterally administered acyclovir. The secondary study objectives are: 1) to define the pharmacokinetic profile of acyclovir in neonates receiving oral valacyclovir and 2) to assess and describe the safety profile of valacyclovir among treated neonates.

Inclusion Criteria:

1. Signed informed consent from parent(s) or legal guardian(s)

2. Maternal history of genital HSV infection

3. Maternal receipt of oral acyclovir, valacyclovir, or famciclovir suppressive therapy for >/= 7 days prior to delivery

4. Gestational age >/= 38 weeks at birth

5. </= 2 days of age at study enrollment*

6. Weight at study enrollment >/= 2,000 grams

   • For purposes of this study, the calendar day of birth is Day of Life 0

Exclusion Criteria:

1. Evidence of neonatal HSV infection
2. Evidence of sepsis
3. Known renal anomalies or dysfunction
4. Maternal genital lesions suspicious for HSV at the time of delivery
5. Infants known to be born to women who are HIV positive (but HIV testing is not required for study entry)
6. Current receipt in the neonate of acyclovir, ganciclovir, famciclovir, or any investigational drugs