What is the recommended dosage of Zovarax (Acyclovir) for treating herpes simplex virus infections?

Zovirax (Acyclovir) Dosing for Herpes Simplex Virus Infections

For recurrent HSV episodes, use acyclovir 800 mg orally twice daily for 5 days, which offers the best balance of efficacy and convenience with only two doses per day. 1, 2

First Episode Genital Herpes

• Treat with acyclovir 200 mg orally 5 times daily for 10 days or until clinical resolution. 3, 4
• This longer duration is critical for first episodes because they are typically more severe and prolonged than recurrences. 3
• For severe disease requiring hospitalization (disseminated infection, encephalitis, pneumonitis, or hepatitis), escalate to acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days or until clinical resolution. 3, 1, 4

Recurrent Episodes (Genital or Oral HSV)

Three equally effective oral regimens are available—choose based on patient adherence preference: 3, 1, 2

• Acyclovir 800 mg orally twice daily for 5 days (best adherence—only 2 doses/day) 3, 1, 2
• Acyclovir 400 mg orally 3 times daily for 5 days 3, 1, 2
• Acyclovir 200 mg orally 5 times daily for 5 days 3, 1, 2

Critical Timing Considerations

• Treatment must be initiated during prodrome or within 2 days of lesion onset for maximum benefit. 1, 5, 4
• Most immunocompetent patients with recurrent disease experience limited benefit when treatment is delayed beyond this window. 3, 5
• Early treatment during prodrome can reduce the proportion of patients who develop full lesions (7% vs 26% with placebo). 5

Chronic Suppressive Therapy

For patients with frequent recurrences (≥6 episodes per year), use acyclovir 400 mg orally twice daily continuously. 3, 1, 4, 2

• This regimen reduces recurrence frequency by at least 75%. 3, 1, 4
• After 1 year of continuous suppressive therapy, discontinue acyclovir to reassess the patient's recurrence rate. 3, 2
• Alternative regimen: acyclovir 200 mg orally 3-5 times daily, with the goal of identifying the lowest dose that provides relief. 3, 4
• Safety and efficacy have been documented for up to 5 years of continuous use. 3

Important Caveat About Suppressive Therapy

• Suppressive therapy does not totally eliminate symptomatic or asymptomatic viral shedding or the potential for transmission. 3
• Acyclovir-resistant strains have been isolated from some persons receiving suppressive therapy, but these have not been associated with treatment failure in immunocompetent patients. 3

Herpes Zoster (Shingles)

Acyclovir 800 mg orally 5 times daily for 7-10 days. 2

• For severe disease or complications, use acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days or until clinical improvement. 1

Pediatric Dosing

Chickenpox (Varicella)

• Children ≥2 years and <40 kg: acyclovir 20 mg/kg orally 4 times daily (maximum 800 mg/dose) for 5 days. 2
• Children >40 kg and adults: acyclovir 800 mg orally 4 times daily for 5 days. 2
• Therapy should be initiated within 24 hours of rash onset for maximum benefit. 2

Mucocutaneous HSV in Children

• Acyclovir 20 mg/kg orally 3 times daily (maximum 400 mg/dose) for 7-14 days. 1
• For severe disease requiring hospitalization: acyclovir 5-10 mg/kg IV every 8 hours for 7-14 days. 1
• For CNS disease: acyclovir 10 mg/kg IV 3 times daily for 21 days. 1

Immunocompromised Patients

Immunocompromised patients require more aggressive therapy with higher doses and longer durations. 1, 4, 6

• For suppression: acyclovir 400 mg orally 3-5 times daily. 1
• For acute treatment: consider starting with 800 mg orally 5 times daily rather than standard dosing. 6
• Be vigilant for acyclovir resistance if lesions persist despite therapy—this is rare in immunocompetent patients but more common in immunocompromised hosts. 1, 6

Acyclovir-Resistant HSV

For documented acyclovir-resistant HSV infection, foscarnet 40 mg/kg IV 3 times daily or 60 mg/kg IV twice daily is the treatment of choice. 1, 6

• If foscarnet fails, consider IV cidofovir or topical cidofovir 1-3% ointment. 6
• Topical trifluridine (TFT) ophthalmic solution applied 3-4 times daily can be used for accessible mucocutaneous lesions. 6

Renal Dose Adjustments

Acyclovir requires dose modification in renal impairment because it is primarily renally excreted. 1, 2

Dosing by Creatinine Clearance:

For 200 mg every 4 hours regimen: 2

• CrCl >10 mL/min: 200 mg every 4 hours (5 times daily)
• CrCl 0-10 mL/min: 200 mg every 12 hours

For 400 mg every 12 hours regimen: 2

• CrCl >10 mL/min: 400 mg every 12 hours
• CrCl 0-10 mL/min: 200 mg every 12 hours

For 800 mg every 4 hours regimen: 2

• CrCl >25 mL/min: 800 mg every 4 hours (5 times daily)
• CrCl 10-25 mL/min: 800 mg every 8 hours
• CrCl 0-10 mL/min: 800 mg every 12 hours

For hemodialysis patients: administer an additional dose after each dialysis session. 2

Critical Clinical Pearls

• Oral acyclovir is significantly more effective than topical formulations—topical acyclovir provides no improvement in systemic symptoms and should not be used as primary therapy. 5, 4
• Acyclovir neither eradicates latent virus nor affects subsequent risk, frequency, or severity of recurrences after discontinuation. 5
• Ensure adequate hydration during therapy, as acyclovir is primarily renally excreted. 1
• Monitor for neutropenia, which is the most common toxicity in children receiving acyclovir. 1
• Patients should abstain from sexual activity while lesions are present, though transmission can occur during asymptomatic periods. 3, 5, 4
• Women of childbearing age with genital herpes should inform obstetric providers about their infection due to neonatal transmission risk. 3, 4