Is Acyclovir Safe in Pregnancy

Status

caution Last reviewed: 2026-05-16 · Confidence: moderate

Reason

Pregnancy data are limited but reassuring; use only if benefit outweighs risk and clinician review is needed.

Drug Information

Brand Name
Zovirax
Generic Name
acyclovir
Drug Class
antiviral (herpesvirus nucleoside analog)
FDA Category
B
Rx Status
prescription

Safe Amount

Dosage must be determined by your provider based on individual risk/benefit.

Effects

Pregnancy
FDA labeling says use during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Mother
May be used when needed for serious herpes or varicella infections; kidney side effects are a concern, especially with dehydration or renal disease.
Baby
Placental transfer occurs; limited human data show no clear increase in birth defects, but rare risks cannot be ruled out.

Trimester Notes

1st Trimester
Limited registry data are reassuring, but data are not enough to rule out rare risks; use only if needed.
2nd Trimester
No special trimester warning in official labeling; continued use should be provider-directed based on benefit and risk.
3rd Trimester
May be used near term when prescribed for genital herpes suppression to reduce outbreaks at delivery; provider should guide dosing.

Risk-Benefit Note

For antivirals, the benefit of treating maternal herpes or varicella infection may outweigh the potential fetal risk. Do not stop or start without provider guidance.

Conditions & Warnings

  • Consult OB/GYN or prescriber
  • Herpes simplex infection
  • Genital herpes suppression near delivery
  • Varicella-zoster infection
  • Renal impairment
  • Dehydration

Alternatives

  • Valacyclovir
  • Famciclovir
  • Non-drug measures per OB/GYN guidance

References

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