Treatment of Varicella (Chickenpox) in Adults
Adults diagnosed with varicella should receive oral acyclovir 800 mg five times daily for 5 days, initiated within 24 hours of rash onset for maximum benefit. 1, 2
Timing is Critical for Treatment Efficacy
- Treatment must begin within 24 hours of rash onset to achieve meaningful clinical benefit, including reduced time to complete crusting (7.4 days reduced to 5.6 days), decreased fever duration by half a day, and 46% reduction in maximum lesion count 2, 3
- Therapy initiated 25-72 hours after rash onset provides no measurable benefit in otherwise healthy adults with uncomplicated varicella 2
- The dramatic difference in efficacy based on timing reflects the natural progression of viral replication, which peaks early in the disease course 4, 3
Standard Dosing Regimen
- Oral acyclovir 800 mg every 4 hours (five times daily) for 5 days is the FDA-approved regimen for adults and children over 40 kg 1
- For children 2 years and older weighing ≤40 kg: 20 mg/kg per dose four times daily (80 mg/kg/day) for 5 days 1
Renal Dose Adjustments
- Creatinine clearance 10-25 mL/min: 800 mg every 8 hours 1
- Creatinine clearance 0-10 mL/min: 800 mg every 12 hours 1
- Hemodialysis patients: Administer additional dose after each dialysis session due to 60% reduction in plasma concentrations during 6-hour dialysis 1
Complicated Varicella Requiring IV Therapy
- Intravenous acyclovir is indicated for varicella pneumonia (the most common serious complication in adults), other visceral dissemination, or immunocompromised patients regardless of timing 1, 4, 5
- Immunocompromised patients should receive antiviral therapy regardless of when treatment is initiated due to higher risk of disseminated infection 6
- IV therapy should continue for 7-10 days minimum in complicated cases 1
Special Population: Pregnant Women
- Acyclovir is FDA Pregnancy Category B with no increased birth defects documented in 596 first-trimester exposures 6
- While oral acyclovir can be used with caution in pregnancy, the evidence base is more limited than for non-pregnant adults 5
- Varicella-zoster immune globulin (VZIG) is strongly preferred for pregnant women exposed to varicella, administered within 96 hours of exposure 7, 6
Post-Exposure Prophylaxis (Not Treatment)
- For susceptible adults exposed to varicella: VZIG within 96 hours of exposure is first-line prophylaxis 7, 6
- If VZIG unavailable or >96 hours post-exposure: acyclovir 20 mg/kg (maximum 800 mg) four times daily for 5-7 days, initiated 7-10 days after exposure 6
- This prophylactic timing (7-10 days post-exposure) corresponds to the late incubation period when secondary viremia begins 6
Important Clinical Caveats
- The low frequency of serious complications (pneumonia, encephalitis, death) in otherwise healthy adults means treatment primarily reduces symptom duration and severity rather than preventing life-threatening outcomes 2
- No data support routine use in healthy children under 13 years due to marginal benefit and cost considerations 8
- Acyclovir has a high therapeutic index and excellent safety profile in adults 5
- Do not confuse varicella (chickenpox) treatment with herpes zoster (shingles) treatment, which has a 72-hour window rather than 24-hour window for efficacy 9