How should a pregnant woman with varicella rash appearing within 24 hours be treated—what oral or intravenous acyclovir regimen is recommended and when is varicella‑zoster immune globulin (VZIG) indicated?

Treatment of Varicella in Pregnancy

For a pregnant woman presenting with varicella rash within 24 hours, initiate oral acyclovir 800 mg five times daily for 5 days immediately; if severe complications such as pneumonia develop, switch to intravenous acyclovir 10–15 mg/kg every 8 hours. 1, 2

Oral Acyclovir Regimen for Active Varicella

• The standard oral regimen is acyclovir 800 mg five times daily for 5 days, started within 24 hours of rash onset. 1, 3
• Treatment beyond the 24-hour window loses clinical benefit in otherwise healthy pregnant women, so prompt initiation is critical. 4, 1
• The FDA labels acyclovir as Category B in pregnancy, with a registry of 596 first-trimester exposures showing no increased birth defects compared to the general population (2.3% vs. 3.2%). 1

Intravenous Acyclovir for Severe Complications

• If varicella pneumonitis or other serious complications develop, admit the patient and administer intravenous acyclovir 10–15 mg/kg (or 500 mg/m²) every 8 hours for 5–10 days. 2
• Pregnant women are at higher risk for severe varicella and pneumonia compared to non-pregnant adults, making close monitoring essential. 1, 5
• Oral acyclovir has poor bioavailability in severe disease, so intravenous administration is necessary for complicated cases. 2

Varicella-Zoster Immune Globulin (VZIG) Indications

Post-Exposure Prophylaxis (Not Active Disease)

• VZIG is indicated for post-exposure prophylaxis in seronegative or immunity-unknown pregnant women, not for treatment of active varicella rash. 1
• Administer VZIG within 96 hours of exposure (ideally as soon as possible) to prevent severe maternal complications; it reduces infection rates from >70% to ≈30%. 1
• VZIG does not prevent viremia, fetal infection, or congenital varicella syndrome—its sole purpose is preventing severe maternal disease. 1
• If VZIG is given, monitor for prodromal symptoms and rash for 28 days (extended from 21 days because VZIG prolongs the incubation period). 1

Neonatal VZIG Administration

• The highest-risk period for neonatal varicella is when maternal rash appears between 5 days before delivery and 2 days after delivery, with historical neonatal mortality of ≈31% without intervention. 1, 2
• Administer VZIG to all neonates born during this peripartum window immediately after birth, regardless of whether the mother received VZIG. 1, 2
• Some evidence suggests combining neonatal VZIG (500 mg/kg at birth) with prophylactic intravenous acyclovir (5 mg/kg every 8 hours starting 7 days after maternal rash onset) may be more effective than VZIG alone, though this is based on limited data. 6

Critical Timing and Common Pitfalls

• The 24-hour window for initiating acyclovir in active varicella is strict; treatment started later does not confer clinical advantage. 4, 1
• Failing to administer VZIG within 96 hours of exposure in seronegative pregnant women is a critical error that compromises effectiveness. 1
• Do not withhold neonatal VZIG even if the mother received VZIG, when maternal rash occurs in the peripartum risk period (5 days before to 2 days after delivery). 1
• Acyclovir does not prevent varicella transmission or reduce isolation duration; patients must remain isolated until all lesions have crusted over. 4

Monitoring and Follow-Up

• Perform detailed ultrasound and appropriate follow-up for all pregnant women who develop varicella to screen for fetal consequences of infection. 2
• Inform neonatal health care providers of peripartum varicella exposure to optimize early neonatal care with VZIG and monitoring. 2
• Observe closely for signs of maternal pneumonitis, which requires immediate escalation to intravenous acyclovir and hospital admission. 2, 5

Alternative Prophylaxis Considerations

• Recent evidence suggests oral acyclovir prophylaxis (after exposure but before rash) may be as effective as VZIG in preventing maternal chickenpox (30.8% vs. 36.6% infection rates, p=0.32), though this is not yet standard practice in most guidelines. 7
• If oral acyclovir is considered for prophylaxis, obtain VZV IgG serology so the antiviral can be discontinued promptly if the patient is seropositive. 1