Acyclovir Dosing for Herpes Simplex Virus Infection
For first-episode genital herpes in otherwise healthy adults, treat with acyclovir 200 mg orally 5 times daily for 7-10 days, or alternatively 400 mg orally twice daily for 5-14 days. 1, 2
Clinical Presentation-Based Dosing Algorithm
First Clinical Episode (Primary or Non-Primary)
- Standard genital herpes: Acyclovir 200 mg orally 5 times daily for 7-10 days until clinical resolution 1
- Herpes proctitis: Acyclovir 400 mg orally 5 times daily for 10 days 1
- Moderate-to-severe gingivostomatitis: Start with acyclovir 5-10 mg/kg IV every 8 hours, then switch to oral when lesions regress 3
- Mild gingivostomatitis: Acyclovir 20 mg/kg (max 400 mg/dose) orally 3 times daily for 5-10 days 3
The FDA-approved labeling supports 200 mg every 4 hours (5 times daily) for 10 days for initial genital herpes 2. This regimen has demonstrated significant reduction in viral shedding, lesion duration, and symptom severity in randomized controlled trials 4.
Recurrent Episodes
Three equivalent options for immunocompetent patients (treatment should begin at earliest prodrome) 1:
- Acyclovir 200 mg orally 5 times daily for 5 days, OR
- Acyclovir 400 mg orally 3 times daily for 5 days, OR
- Acyclovir 800 mg orally 2 times daily for 5 days
Important caveat: Most immunocompetent patients with recurrent disease derive minimal benefit from episodic treatment unless initiated during prodrome or within 2 days of lesion onset 1. Early patient-initiated therapy appears most favorable 5.
Suppressive Therapy
For patients with ≥6 recurrences per year: Acyclovir 400 mg orally twice daily 1
- Alternative regimen: 200 mg orally 3-5 times daily (titrate to lowest effective dose) 1
- Reduces recurrence frequency by ≥75% 1
- Safety documented for up to 5 years of continuous use 1
- Reassess after 1 year to determine ongoing need 1, 2
The FDA label supports 400 mg twice daily for up to 12 months with mandatory re-evaluation 2.
Severe or Complicated Disease
For disseminated infection, encephalitis, pneumonitis, hepatitis, or hospitalized patients: Acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days until clinical resolution 1
- CNS disease in children (non-neonatal): 10 mg/kg IV every 8 hours for 21 days 3
- HSV meningitis: 10 mg/kg IV every 8 hours until fever/headache resolve, then valacyclovir 1 g TID to complete 14 days 6
- Neonatal CNS disease: 20 mg/kg IV every 8 hours for 21 days with repeat CSF HSV PCR at days 19-21 3
Critical distinction: HSV encephalitis requires 14-21 days of IV acyclovir due to high morbidity/mortality 6. Recent modeling suggests current dosing may be suboptimal, with QID dosing or extended infusion durations (1.5-2 hours) potentially improving CNS penetration while maintaining safety 7.
Renal Dosing Adjustments
Mandatory dose modification for renal impairment 2:
| Normal Dose | CrCl (mL/min) | Adjusted Dose |
|---|---|---|
| 200 mg q4h | 0-10 | 200 mg q12h |
| 400 mg q12h | 0-10 | 200 mg q12h |
| 800 mg q4h | 10-25 | 800 mg q8h |
| 800 mg q4h | 0-10 | 800 mg q12h |
Hemodialysis: Administer additional dose after each dialysis session (60% decrease in plasma concentrations during 6-hour dialysis) 2.
Alternative Agents
Valacyclovir (better bioavailability, 3-5× higher acyclovir exposure):
- First episode: 1000 mg twice daily for 10 days (equivalent efficacy to acyclovir 200 mg 5×/day) 8
- Adults/adolescents with mucocutaneous HSV: 1 g twice daily 3
Acyclovir-resistant HSV (primarily in immunocompromised patients):
- Foscarnet 40 mg/kg IV every 8 hours or 60 mg/kg IV every 12 hours 3
- Pritelivir under investigation for resistant cases 6, 9
Common Pitfalls
- Inadequate dosing frequency: The 5-times-daily regimen requires dosing every 4 hours while awake—poor adherence undermines efficacy
- Delayed initiation: Benefit diminishes substantially if treatment starts >48-72 hours after symptom onset 1
- Inappropriate suppressive therapy: Not indicated for patients with <6 recurrences/year
- Topical acyclovir: Substantially less effective than oral therapy and should be avoided 1, 5
- Renal toxicity: Monitor for acute kidney injury, particularly with IV dosing or supra-therapeutic doses 2, 10—maintain adequate hydration
- Pregnancy considerations: Acyclovir has more safety data than valacyclovir; prophylaxis after 36 weeks gestation (400 mg TID) reduces cesarean section rates 11
Evidence Quality
The dosing recommendations derive primarily from CDC STD treatment guidelines 1 and FDA labeling 2, representing the highest-quality evidence for this indication. The 2022 CDC guidelines review 6 provides the most recent comprehensive analysis, though specific dosing recommendations remain consistent with earlier guidelines. Pediatric and HIV-specific dosing comes from 2009 NIH/CDC opportunistic infection guidelines 3.