Acyclovir Dosing for HSV-1 and HSV-2 Infections
For HSV-1 oral lesions (herpes labialis) in healthy adults, use acyclovir 400 mg orally three times daily for 5 days, and for HSV-2 genital herpes, use acyclovir 400 mg orally twice daily for 5-14 days depending on whether it's a first episode or recurrence. 1
HSV-1 Oral Lesions (Herpes Labialis)
Mild Symptomatic Gingivostomatitis
- Acyclovir 400 mg orally three times daily for 5-10 days 2
- Treatment should be initiated at the earliest sign or symptom (prodrome) for maximum benefit 1
- Alternative: Valacyclovir 1 g orally twice daily (approved for adults and adolescents) 2
Moderate to Severe Gingivostomatitis
- Start with acyclovir 5-10 mg/kg IV three times daily 2
- Once lesions begin to regress, switch to oral acyclovir and continue until complete healing 2
HSV-2 Genital Herpes
First Clinical Episode
- Acyclovir 200 mg orally 5 times daily for 7-10 days (or until clinical resolution) 3, 1
- Alternative FDA-approved regimen: Acyclovir 400 mg orally twice daily for 5-14 days 2
- For severe first episodes requiring hospitalization: Acyclovir 5 mg/kg IV every 8 hours 3
Recurrent Episodes (Episodic Treatment)
- Acyclovir 400 mg orally twice daily for 5 days 1
- Alternative regimens:
- Initiate therapy at the earliest sign or symptom (ideally during prodrome) to maximize benefit 1
- A 2-day course of acyclovir 800 mg three times daily has also shown efficacy 4
Chronic Suppressive Therapy
For patients with frequent recurrences (≥6 episodes per year):
- Acyclovir 400 mg orally twice daily 3, 1
- Alternative: 200 mg orally 3-5 times daily 3
- Continue for up to 12 months, then re-evaluate the need for ongoing suppression 1
- Suppressive therapy reduces recurrence frequency by at least 75% 3
Important Clinical Considerations
Timing of Treatment
The evidence consistently emphasizes that early initiation is critical—treatment started within 24-48 hours of symptom onset provides the most benefit 1, 5. For recurrent episodes, patient-initiated therapy at the first sign of prodrome may abort the episode entirely in some cases 6.
Renal Impairment
Dosage adjustment is mandatory in renal dysfunction 1:
- For CrCl 10-25 mL/min: reduce frequency to every 8-12 hours depending on indication
- For CrCl 0-10 mL/min: reduce to every 12 hours
- After hemodialysis: administer an additional dose 1
Common Pitfalls
- Avoid topical acyclovir monotherapy—it is substantially less effective than oral formulations and does not address systemic symptoms 3, 6
- Do not assume treatment prevents transmission—patients remain infectious during asymptomatic viral shedding 1
- Acyclovir does not eradicate latent virus or prevent future recurrences once discontinued 3
Resistance Considerations
Acyclovir-resistant HSV strains occur primarily in immunocompromised patients, especially those with advanced HIV 1, 7. If poor clinical response occurs despite adequate dosing and adherence, consider viral resistance and switch to foscarnet 40 mg/kg IV three times daily 2.
Pregnancy and Lactation
Acyclovir is Pregnancy Category B with no documented teratogenic effects in humans 1. A prospective registry of 749 first-trimester exposures showed birth defect rates approximating the general population 1. However, use only when potential benefit justifies potential risk. Acyclovir concentrates in breast milk at 0.6-4.1 times plasma levels, potentially exposing nursing infants to up to 0.3 mg/kg/day 1.