At what gestational age should Valtrex (valacyclovir) be started in pregnant women with a history of Herpes Simplex Virus (HSV)?

Valacyclovir Timing for HSV in Pregnancy

Valacyclovir suppressive therapy should be started at 36 weeks' gestation in pregnant women with a history of genital herpes to reduce viral shedding, recurrences, and cesarean deliveries. 1

Risk Assessment and Rationale

Neonatal herpes transmission risk varies significantly based on timing and type of maternal HSV infection:

• Highest risk (30-50%): Women who acquire genital herpes near delivery time 1, 2
• Lower risk (approximately 3%): Women with recurrent herpes at term or who acquired HSV during first half of pregnancy 2

Recommended Management Algorithm

1. Timing of Valacyclovir Initiation:

   • Start at 36 weeks' gestation 1, 3, 4
   • Continue until delivery

2. Dosing Regimen:

   • Valacyclovir 500 mg twice daily 1, 3, 4
   • Alternative: Acyclovir 400 mg three times daily 1

3. Clinical Benefits:

   • Significantly reduces clinical HSV recurrences (10.5% vs 27.3% with placebo) 3
   • Decreases HSV shedding at delivery (2% vs 9% with placebo) 4
   • Reduces cesarean deliveries for active HSV lesions (4% vs 13% with placebo) 4
   • Meta-analysis shows 75% reduction in clinical recurrences at delivery 5

Evidence Quality and Considerations

Multiple randomized clinical trials demonstrate that suppressive therapy starting at 36 weeks significantly reduces:

• Viral shedding
• Clinical recurrences
• Need for cesarean deliveries 1, 3, 4, 5

Pharmacokinetic data shows valacyclovir provides higher plasma acyclovir levels than acyclovir itself, with significantly higher peak concentrations 6.

Safety Profile

• Acyclovir remains category B in pregnancy 1
• Current registry findings do not indicate increased risk for major birth defects with acyclovir treatment compared to general population 1
• No significant maternal, obstetric, or neonatal complications have been observed in clinical trials of valacyclovir use in late pregnancy 3, 4

Important Caveats

• Earlier initiation (28 weeks) has been studied in one trial from Uganda, showing decreased risk of preterm birth, but additional data are needed to support this practice 1
• A case-control study showed increased odds for gastroschisis with antiherpes medications used between one month prior to conception and third month of pregnancy, but significant demographic differences and possible recall bias limit these findings 1
• Routine administration of suppressive therapy throughout pregnancy is not currently recommended 1

Labor and Delivery Management

• All women should be examined at onset of labor for symptoms of genital herpes 1, 2
• Cesarean delivery is recommended for women with active genital lesions or prodromal symptoms at the onset of labor 2, 7
• Vaginal delivery is permitted if no clinical recurrence or prodromal symptoms are present 4

Starting valacyclovir at 36 weeks' gestation represents the optimal balance between maximizing protection against recurrence while minimizing medication exposure during pregnancy.