Recommended Duration of Acyclovir for Adult Chickenpox
For adults with chickenpox, oral acyclovir should be administered at 800 mg four times daily for 5 days, initiated within 24 hours of rash onset for maximum efficacy. 1
Treatment Duration and Dosing
- The FDA-approved regimen is 800 mg orally four times daily for 5 days for adults and children over 40 kg with chickenpox 1
- A 5-day course is sufficient and provides equivalent benefit to a 7-day course, with no additional clinical advantage from extended therapy 2
- Treatment must be initiated within 24 hours of rash onset to achieve meaningful clinical benefit 3, 1
Critical Timing Considerations
- Therapy initiated after 24 hours of rash onset provides minimal to no benefit in immunocompetent adults 4
- Early treatment (within 24 hours) reduces time to 100% crusting from 7.4 to 5.6 days and decreases maximum lesion count by 46% 4
- Late therapy (25-72 hours after rash onset) has no effect on the course of uncomplicated illness in immunocompetent adults 4
Special Population Exceptions
Immunocompromised Patients
- Immunocompromised adults require intravenous acyclovir regardless of timing, as they face substantially higher risk of disseminated infection and mortality 5, 3
- Treatment should continue at least until all lesions have scabbed 6
Pregnant Women
- Acyclovir is FDA Pregnancy Category B with no increased birth defects documented in 596 first-trimester exposures 5
- For pregnant women with active chickenpox, the same 5-day oral regimen applies if disease is mild, though IV acyclovir should be considered for serious complications like pneumonia 6
Common Pitfalls to Avoid
- Do not confuse chickenpox treatment with herpes zoster (shingles) treatment, which uses 800 mg five times daily for 7-10 days 1
- Do not extend therapy beyond 5 days in immunocompetent patients, as this provides no additional benefit and was specifically studied 2
- Do not initiate treatment after 24 hours in otherwise healthy adults expecting significant clinical benefit, as efficacy is lost 4
- Acyclovir does not prevent transmission or reduce school absence duration, so isolation precautions must continue until all lesions are crusted 6