What is the recommended acyclovir dosing regimen for a pregnant woman with herpes labialis?

Acyclovir Dosing for Cold Sores in Pregnancy

For pregnant women with herpes labialis (cold sores), acyclovir 400 mg orally three times daily for 7-10 days is the recommended first-line treatment, with an excellent safety profile throughout pregnancy. 1, 2

First-Line Treatment Regimens

Oral acyclovir is the preferred antiviral for cold sores during pregnancy, with the following evidence-based options:

• Acyclovir 400 mg orally three times daily for 7-10 days is the CDC-recommended first-line regimen for acute herpes episodes in pregnancy 1, 2
• Valacyclovir 1 g orally twice daily for 7-10 days is an equally safe alternative with more convenient dosing 1, 2
• Acyclovir 200 mg orally five times daily for 5-10 days is effective but requires more frequent dosing, which may reduce adherence 3

Safety Evidence in Pregnancy

The safety data for acyclovir in pregnancy is robust and reassuring:

• CDC registry findings show no increased risk of major birth defects after acyclovir or valacyclovir treatment compared to the general population 4, 1, 2
• No consistent pattern of adverse pregnancy outcomes has been reported after prenatal acyclovir exposure 1, 2
• Both medications are considered safe throughout all trimesters of pregnancy 1
• Acyclovir pharmacokinetics in late pregnancy are similar to non-pregnant adults, with a maternal/infant plasma ratio of 1.3 at delivery, indicating no fetal accumulation 5

Critical Timing Considerations

Treatment must be initiated during the prodromal phase (tingling, burning) or within 24 hours of lesion onset to achieve optimal therapeutic benefit, as peak viral titers occur in the first 24 hours after lesion appearance 1, 6, 7. Starting treatment after 48 hours markedly diminishes clinical efficacy 7.

Special Populations and Dose Adjustments

Immunocompromised Pregnant Women (including HIV-positive)

• Higher doses are required: acyclovir 400 mg orally three to five times daily until clinical resolution 4, 1, 2
• These patients experience more prolonged and severe episodes with higher acyclovir resistance rates (7% versus <0.5% in immunocompetent patients) 1, 6
• If lesions persist despite standard therapy, suspect acyclovir resistance and consider IV foscarnet 40 mg/kg every 8 hours 4, 1

Severe or Life-Threatening Maternal HSV Infection

• For disseminated infection, encephalitis, pneumonitis, or hepatitis: acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days is definitively indicated, as benefits clearly outweigh any theoretical risks 4, 2

Suppressive Therapy for Frequent Recurrences

For pregnant women with frequent, severe recurrences of oral herpes:

• Consider suppressive prophylaxis starting at 36 weeks gestation: valacyclovir 1000 mg orally twice daily OR acyclovir 400 mg orally three times daily until delivery 1
• This approach is reserved for women with particularly frequent or severe recurrences that significantly impact quality of life 1
• Routine prophylaxis is not recommended for women with a history of oral herpes but no recurrence during pregnancy 3

Important Clinical Considerations

Oral antiviral therapy is markedly superior to topical agents for treating cold sores; topical antivirals provide only modest benefit and should not be used as primary treatment 1, 6, 7.

Continue treatment until all lesions are fully crusted, which correlates with substantial reduction in viral shedding and transmission risk 1. Do not discontinue therapy at a fixed 7-day interval if lesions remain active 1.

Counseling and Prevention

• Patients remain contagious until all lesions are fully crusted; avoid direct contact (kissing, sharing utensils) during active outbreaks 1
• Even with optimal antiviral therapy, viral shedding persists for approximately 6.4 days with valacyclovir versus 8.1 days without treatment 6
• Counsel patients to identify and avoid personal triggers including UV light exposure, fever, psychological stress, and menstruation 1, 6
• Apply sunscreen (SPF ≥15) or zinc oxide to lips before sun exposure to prevent UV-triggered recurrences 6

Common Pitfalls to Avoid

• Do not delay treatment initiation—efficacy decreases dramatically after the first 24-48 hours of lesion onset 1, 6, 7
• Do not rely on topical acyclovir alone during pregnancy; oral therapy is significantly more effective 1, 6, 7
• Do not use lower doses in immunocompromised pregnant patients—they require 400 mg three to five times daily 4, 1
• Do not discontinue therapy prematurely—treat until complete crusting occurs, not just for a fixed duration 1