What is the maximum dose of Acyclovir (an antiviral medication) that can be taken during pregnancy?

Maximum Dose of Acyclovir in Pregnancy

For acute first-episode genital herpes during pregnancy, the maximum recommended dose is acyclovir 400 mg orally three times daily for 7-10 days, while for life-threatening maternal HSV infections (disseminated infection, encephalitis, pneumonitis, or hepatitis), intravenous acyclovir 5 mg/kg every 8 hours is indicated. 1, 2

Dosing by Clinical Indication

First-Episode Genital Herpes

• Acyclovir 400 mg orally three times daily for 7-10 days is the standard treatment for acute first-episode genital herpes during pregnancy 1, 2
• An alternative regimen is valacyclovir 1 g orally twice daily for 7-10 days 1, 2

Suppressive Therapy (Starting at 36 Weeks)

• Acyclovir 400 mg orally three times daily from 36 weeks gestation until delivery for women with recurrent genital herpes 2
• Alternative: valacyclovir 1000 mg orally twice daily 2

Life-Threatening Maternal HSV Infection

• Intravenous acyclovir 5 mg/kg every 8 hours is definitively indicated for disseminated infection, encephalitis, pneumonitis, or hepatitis 1, 2
• This represents the highest dose used in pregnancy and is reserved for severe, life-threatening maternal disease 3

Immunocompromised Patients

• Acyclovir 400 mg orally three to five times daily may be needed for immunocompromised pregnant women with prolonged or severe HSV episodes 1
• If lesions persist during treatment, acyclovir resistance should be suspected 1, 2

Safety Profile

• Current registry findings show no increased risk for major birth defects after acyclovir treatment compared with the general population 1
• No consistent pattern of abnormalities has emerged from registry data, providing reassurance for prenatal exposure 1
• Acyclovir crosses the placenta, achieving cord blood concentrations similar to maternal blood levels at delivery, but there is no fetal accumulation (mean maternal/infant plasma ratio at delivery is 1.3) 4

Critical Context for Dosing Decisions

Transmission Risk

• The risk of neonatal transmission is 30-50% for primary HSV infection acquired near delivery 2
• The risk is only ≤3% for women with recurrent herpes at term 1, 2

Important Caveats

• Do not use systemic acyclovir for routine suppression before 36 weeks gestation in women without life-threatening disease, as older guidelines recommended against this practice 3, 1
• Viral cultures during pregnancy do not predict shedding at delivery and are not routinely indicated 3, 1
• The benefits of IV acyclovir for life-threatening maternal infections clearly outweigh any theoretical risks 1, 2

Pharmacokinetic Considerations

• Peak and trough plasma concentrations in pregnant women are lower compared to non-pregnant adults but remain effective 5
• Steady-state peak levels with 400 mg every 8 hours are approximately 3.3 ± 1.0 μmol/L, which exceeds the inhibitory dose needed for HSV 4
• Acyclovir is concentrated in amniotic fluid but does not accumulate in the fetus 4