What is the recommended oral acyclovir dosing for herpes zoster in a patient with painful dermatomal rash, including adjustments for elderly, immunocompromised or severe disease and for varying degrees of renal impairment?

Acyclovir Dosing for Herpes Zoster (Shingles)

For a patient presenting with dermatomal pain, numbness, and tingling consistent with herpes zoster, the standard oral acyclovir dose is 800 mg five times daily for 7 days, initiated within 72 hours of rash onset for maximum benefit. 1, 2

Standard Dosing for Immunocompetent Adults

• Acyclovir 800 mg orally five times daily for 7 days is the FDA-approved and guideline-recommended regimen for herpes zoster 1, 2
• Treatment must be started within 72 hours of rash onset, with greatest efficacy when initiated within 48 hours 1, 3, 4
• This regimen significantly shortens time to lesion scabbing, healing, cessation of pain, and reduces duration of new lesion formation 2, 3, 4

Dosing Adjustments for Special Populations

Elderly Patients (≥50 years)

• Use the same dose (800 mg five times daily for 7 days) but monitor closely for adverse effects 2, 5
• Elderly patients show greater clinical benefit from treatment, particularly in pain reduction 2
• Dosage reduction may be required if underlying renal impairment exists 2

Immunocompromised Patients

• For severe disease requiring hospitalization: Acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days or until clinical improvement 6
• After clinical improvement, transition to oral therapy and continue until complete healing 6
• Immunocompromised patients may require more aggressive and prolonged therapy 1

Renal Impairment Adjustments

• Acyclovir clearance is dependent on renal function and requires dose adjustment 2
• Ensure adequate hydration as acyclovir is primarily renally excreted 6
• The half-life and total body clearance are significantly affected by reduced renal function 2

Treatment Duration Considerations

• Standard 7-day course is sufficient for most immunocompetent patients 2, 3, 7
• Extending treatment to 21 days offers only slight additional benefit and does not reduce postherpetic neuralgia frequency 7
• For immunocompromised patients with persistent or recalcitrant disease, prolonged treatment may be necessary 1

Alternative Antiviral Options

• Valacyclovir 1000 mg three times daily for 7 days offers simpler dosing with superior pain resolution compared to acyclovir 8, 5
• Valacyclovir accelerates resolution of herpes zoster-associated pain by 23% compared to acyclovir at day 29 8
• Famciclovir 500 mg three times daily for 7 days provides similar efficacy with less frequent dosing 1

Critical Timing and Efficacy Points

• No significant hastening of rash healing occurs when therapy starts >48 hours after rash onset 3
• Treatment within 24 hours of rash onset provides maximum clinical benefit 2
• Acyclovir significantly reduces acute pain during treatment (p=0.02) but has variable effects on postherpetic neuralgia prevention 3, 7

Common Pitfalls to Avoid

• Do not use topical acyclovir alone - it has not been shown to be helpful for VZV infections 1
• Do not delay treatment - efficacy dramatically decreases after 72 hours from rash onset 1, 3
• Do not underdose - the 800 mg five times daily regimen is critical; lower doses are ineffective for herpes zoster 2
• Do not forget renal adjustment - failure to adjust for renal impairment can lead to toxicity 2

Monitoring and Follow-up

• Monitor for neutropenia, the most common toxicity in patients receiving acyclovir 6
• Assess for adequate hydration throughout treatment course 6
• Watch for late sequelae including dry eye and corneal anesthesia with neurotrophic keratitis in ophthalmic zoster 1