Acyclovir Prophylaxis for Varicella

Introduction to Prophylaxis

The Centers for Disease Control and Prevention recommends acyclovir 20 mg/kg (maximum 800 mg) orally four times daily for 5-7 days, initiated 7-10 days after exposure when varicella-zoster immune globulin (VZIG) is unavailable or if more than 96 hours have passed since exposure 1

VZIG remains the first-line prophylaxis for susceptible high-risk individuals (immunocompromised, pregnant women, neonates) after varicella exposure, administered within 96 hours of exposure at 125 units/10 kg body weight (maximum 625 units) intramuscularly 1, 2, 3, 4

The recommended dosing regimen for acyclovir prophylaxis is 20 mg/kg body weight (maximum 800 mg per dose) orally four times daily for 5-7 days 1
Acyclovir prophylaxis should be initiated 7-10 days after exposure, corresponding to the late incubation period when secondary viremia begins 1, 5
The target population for acyclovir prophylaxis includes susceptible immunocompromised patients and other high-risk individuals without evidence of immunity 1, 2

For pregnant women, VZIG is strongly preferred within 96 hours of exposure 2, 6
If VZIG is unavailable, oral acyclovir 10 mg/kg four times daily for 7 days can be considered for pregnant women 5
Acyclovir is FDA Category B with no increased birth defects in 596 first-trimester exposures 6
For HIV-infected patients, the recommended prophylaxis after exposure is 20 mg/kg (maximum 800 mg) four times daily for 5-7 days 1
Note that data on acyclovir preventing chickenpox in HIV-infected individuals are limited 7

The duration of protection for acyclovir prophylaxis only covers the treatment period, unlike VZIG which provides approximately 3 weeks of protection 2, 3