What is the recommended Aciclovir dosage for an adult patient with a viral infection and normal renal function?

Aciclovir Dosage for Adult Patients with Normal Renal Function

For adult patients with normal renal function, the recommended aciclovir dosage depends on the specific viral infection being treated, with oral doses ranging from 200-800 mg multiple times daily for herpes simplex infections and intravenous doses of 5-10 mg/kg every 8 hours for severe disease or encephalitis.

Herpes Simplex Virus (HSV) Infections

First Clinical Episode - Genital Herpes

• Aciclovir 200 mg orally 5 times daily for 7-10 days until clinical resolution is the standard CDC-recommended regimen 1
• For herpes proctitis specifically, increase to aciclovir 400 mg orally 5 times daily for 10 days 1

Recurrent Genital or Oral HSV Episodes

The CDC provides three equally effective options 2, 3:

• Aciclovir 200 mg orally 5 times daily for 5 days, OR
• Aciclovir 400 mg orally 3 times daily for 5 days, OR
• Aciclovir 800 mg orally twice daily for 5 days

Critical timing consideration: Treatment must be initiated during the prodrome or within 2 days of lesion onset for maximum benefit 1, 3. Most immunocompetent patients with recurrent disease receive limited benefit if treatment is delayed beyond this window 1.

Chronic Suppressive Therapy

• Aciclovir 400 mg orally twice daily is the recommended suppressive regimen for patients with frequent recurrences (≥6 episodes per year) 1, 2
• This reduces recurrence frequency by at least 75% 1, 2
• Alternative regimen: Aciclovir 200 mg orally 3-5 times daily, titrating to find the lowest effective dose 1, 2
• After 1 year of continuous therapy, discontinue aciclovir to reassess the patient's recurrence rate 1

Severe HSV Disease Requiring Hospitalization

• Aciclovir 5-10 mg/kg intravenously every 8 hours for 5-7 days or until clinical improvement 1, 2
• This applies to severe mucocutaneous disease, disseminated infection, or any HSV complication requiring hospitalization 2

HSV Encephalitis

Aciclovir 10 mg/kg intravenously every 8 hours for 14-21 days is the standard treatment for HSV encephalitis 1. This dosing has been shown in randomized trials to reduce mortality from approximately 70% to 20-30% 1.

• Some experts recommend 15 mg/kg every 8 hours for VZV encephalitis if renal function is normal, though most clinicians use 10 mg/kg due to renal toxicity concerns 1
• Treatment should be initiated empirically within 6 hours of admission if CSF or imaging findings suggest viral encephalitis, even before HSV PCR confirmation 1
• Delays beyond 48 hours between hospital admission and treatment initiation significantly worsen outcomes 1

Varicella-Zoster Virus (VZV) - Herpes Zoster

Immunocompromised Patients

• Aciclovir 800 mg orally 5 times daily for 7-10 days 4
• Alternative dosing based on body surface area: 500 mg/m² every 8 hours 4

Severe or Disseminated Disease

• Aciclovir 10 mg/kg intravenously every 8 hours for 7-10 days 4
• Alternative: 500 mg/m² intravenously every 8 hours 4

VZV Encephalitis

• Aciclovir 10-15 mg/kg intravenously three times daily for up to 14 days 1
• A short course of corticosteroids (e.g., prednisolone 60-80 mg daily for 3-5 days) is often added due to the inflammatory nature of VZV CNS disease 1

Important Clinical Considerations

Hydration and Renal Monitoring

• Ensure adequate hydration as aciclovir is primarily renally excreted 2
• Monitor renal function closely, especially with intravenous administration 1
• The dose must be adjusted in patients with pre-existing renal impairment 1

Immunocompromised Patients

• May require higher doses (400 mg orally 3-5 times daily) and longer treatment duration (14 days or until complete resolution) 2
• Prolonged episodes with extensive disease are common in this population 1
• Be vigilant for aciclovir resistance if lesions persist despite therapy 2

Aciclovir-Resistant HSV

• Foscarnet 40 mg/kg intravenously 3 times daily OR 60 mg/kg twice daily is the treatment of choice for aciclovir-resistant infections 2, 5
• Resistance is primarily seen in immunocompromised patients receiving prolonged or suppressive therapy 1, 5

Common Pitfalls to Avoid

• Do not use topical aciclovir as primary therapy—it is substantially less effective than oral formulations and provides no improvement in systemic symptoms 1, 3
• Do not delay treatment in suspected HSV encephalitis waiting for PCR confirmation—empiric treatment within 6 hours significantly improves outcomes 1
• Do not use high-dose valaciclovir (8 g/day) in immunosuppressed patients due to risk of hemolytic-uremic syndrome or thrombotic thrombocytopenic purpura 2
• Monitor for neutropenia in children receiving aciclovir, as this is the most common toxicity 2