What is the recommended dosage and treatment duration of acyclovir for a patient with a viral infection, such as genital herpes or shingles, and potential impaired renal function?

Acyclovir Dosing for Viral Infections

For genital herpes, use acyclovir 400 mg orally three times daily for 5 days for recurrent episodes, or 400 mg twice daily for chronic suppression; for herpes zoster (shingles), use 800 mg orally five times daily for 7-10 days; and adjust all doses for renal impairment by extending dosing intervals or reducing individual doses based on creatinine clearance. 1

First Episode Genital Herpes

For initial genital herpes infections:

• Acyclovir 200 mg orally 5 times daily for 7-10 days until clinical resolution 2
• Alternatively, acyclovir 400 mg orally 3 times daily for 5-14 days in adults and adolescents 2
• In children <45 kg: acyclovir 20 mg/kg (maximum 400 mg/dose) orally 3 times daily for 5-14 days 2, 1

This regimen shortens viral shedding duration (median 2 days vs 9 days with placebo), accelerates healing (12 days vs 16 days), and reduces symptom duration 3

Recurrent Genital Herpes Episodes

For symptomatic recurrences (when treatment initiated within 2 days of onset):

• Acyclovir 400 mg orally 3 times daily for 5 days 1
• Alternative: 800 mg orally twice daily for 5 days 2, 1
• Alternative: 200 mg orally 5 times daily for 5 days 2

A shorter 2-day course (800 mg three times daily for 2 days) significantly reduces lesion duration and viral shedding compared to placebo, offering a convenient alternative 4

Suppressive Therapy for Frequent Recurrences

For patients with ≥6 recurrences per year:

• Acyclovir 400 mg orally twice daily continuously 1, 5
• Alternative: 200 mg orally 3-5 times daily 5

This suppressive regimen reduces recurrence frequency by at least 75% 1, 5. After 1 year of continuous therapy, discontinue acyclovir to reassess the patient's natural recurrence rate 5. Long-term suppression is safe, with minimal toxicity and no significant viral resistance in immunocompetent patients 6, 7

Severe Mucocutaneous HSV Disease

For severe disease requiring hospitalization:

• Acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days or until clinical improvement 1
• After lesions begin regressing, switch to oral acyclovir and continue until complete healing 2

For moderate to severe gingivostomatitis in children, use acyclovir 5-10 mg/kg IV three times daily, then transition to oral therapy 2

Herpes Simplex Encephalitis

For CNS disease:

• Acyclovir 10 mg/kg IV every 8 hours for 14-21 days in adults with normal renal function 2
• In children outside the neonatal period: 10 mg/kg IV three times daily for 21 days 2
• In neonates: consider higher dose of 20 mg/kg IV every 8 hours for 21 days (reduces mortality to 5%) 2

Critical timing consideration: Mortality decreases to 8% if therapy is initiated within 4 days of symptom onset, compared to 28% overall mortality at 18 months 2. Obtain repeat CSF HSV DNA PCR at days 19-21; do not discontinue acyclovir until CSF PCR is negative 2

Herpes Zoster (Shingles)

For immunocompetent patients with shingles:

• Acyclovir 800 mg orally 5-6 times daily for 5-10 days depending on clinical response 6

For severe disease or immunocompromised patients:

• Acyclovir 5-10 mg/kg IV every 8 hours for 5-7 days or until clinical improvement 1

HIV-Infected and Immunocompromised Patients

Special considerations for immunosuppressed patients:

• Use higher suppressive doses: acyclovir 400 mg orally 3-5 times daily 5, 6
• For acute episodes in AIDS patients: 400 mg orally 5 times daily for 5 days, then 400 mg three times daily for 1-2 months, followed by 400 mg twice daily for maintenance 6
• Monitor closely for treatment failure and acyclovir resistance 2
• Suspect resistance if lesions do not begin resolving within 7-10 days of therapy initiation 2

Acyclovir-Resistant HSV

For confirmed acyclovir-resistant infections:

• Foscarnet 40 mg/kg IV three times daily or 60 mg/kg IV twice daily 2, 1
• Alternative for external lesions: topical trifluridine, cidofovir, or imiquimod for 21-28 days 2

Obtain viral culture and susceptibility testing when resistance is suspected 2

Renal Dose Adjustments

Critical monitoring for renal impairment:

• Monitor renal function at treatment initiation and once or twice weekly during high-dose IV therapy 2
• No laboratory monitoring needed for episodic or suppressive oral therapy in patients with normal renal function 2

Dose adjustment strategy:

• For CrCl 25-50 mL/min: extend dosing interval to every 12 hours
• For CrCl 10-25 mL/min: extend dosing interval to every 24 hours
• For CrCl <10 mL/min: reduce dose by 50% and extend interval to every 24 hours
• Ensure adequate hydration, as acyclovir is primarily renally excreted 1

Important Safety Warnings

Avoid these critical errors:

• Never use high-dose valacyclovir (8 g/day) in immunocompromised patients due to risk of thrombotic thrombocytopenic purpura/hemolytic uremic syndrome 2, 1, 5
• Topical acyclovir is substantially less effective than oral therapy and should be avoided 2
• Suppressive therapy reduces but does not eliminate asymptomatic viral shedding or transmission risk 5
• Monitor for neutropenia in children receiving acyclovir 1

Pregnancy Considerations

For pregnant women:

• Acyclovir is the first-choice antiviral in pregnancy based on safety data 2
• Use standard episodic therapy dosing for first episodes and recurrences 2
• Consider suppressive therapy in late pregnancy (after 36 weeks) to reduce cesarean delivery need for recurrent HSV 2