What are the recommended dosing regimens for acyclovir in adults and children for HSV and VZV infections, including adjustments for renal impairment?

Acyclovir Dosing for HSV and VZV Infections

HSV Encephalitis

For HSV encephalitis, adults should receive intravenous acyclovir 10 mg/kg every 8 hours for 14-21 days, while children aged 3 months to 12 years require a minimum of 21 days of treatment due to higher relapse rates (up to 26-29%). 1, 2

Adult Dosing

• Standard dose: 10 mg/kg IV every 8 hours for 14-21 days 1
• Early initiation is critical—mortality decreases to 8% when therapy starts within 4 days of symptom onset, compared to 28% overall mortality at 18 months 1
• Consider repeat CSF PCR at end of therapy; continue treatment if positive 1, 2

Pediatric Dosing

• Children 3 months-12 years: 500 mg/m² IV every 8 hours for minimum 21 days 2
• Children >12 years: 10 mg/kg IV every 8 hours 2
• Neonates: Higher doses (20 mg/kg IV every 8 hours for 21 days) have reduced mortality to 5% 1
• Relapse risk is highest in children 3 months-12 years (up to 29%), mandating the longer 21-day course 2

Monitoring

• Repeat lumbar puncture at 14-21 days to confirm CSF PCR negativity 2
• If CSF remains positive, continue acyclovir with weekly PCR monitoring until negative 2

Herpes Zoster (Shingles)

For herpes zoster, the recommended oral dose is 800 mg five times daily for 7-10 days, initiated within 72 hours of rash onset for optimal efficacy. 3, 4

Oral Dosing

• Adults and children >40 kg: 800 mg orally 5 times daily (every 4 hours while awake) for 7-10 days 3
• Children 2 years and older: 20 mg/kg per dose orally 4 times daily (maximum 800 mg per dose) for 5 days 3
• The 800 mg five times daily regimen is superior to 400 mg five times daily, significantly reducing viral shedding, accelerating healing, and decreasing acute pain severity 4

Timing

• Initiate within 72 hours of rash onset for maximum benefit 3
• Treatment reduces post-zoster pain prevalence, particularly in the first 3 months 4

Genital Herpes

Initial Episode

• 200 mg orally every 4 hours, 5 times daily for 10 days 3

Recurrent Episodes (Intermittent Therapy)

• 200 mg orally every 4 hours, 5 times daily for 5 days 3
• Initiate at earliest prodrome 3

Chronic Suppressive Therapy

• 400 mg orally twice daily for up to 12 months 3
• Alternative regimens: 200 mg 3-5 times daily 3
• Re-evaluate after 1 year to assess continued need 3

Varicella (Chickenpox)

Oral Dosing

• Children 2 years and older: 20 mg/kg per dose orally 4 times daily (80 mg/kg/day) for 5 days 3
• Adults and children >40 kg: 800 mg orally 4 times daily for 5 days 3
• Initiate within 24 hours of rash onset 3

Intravenous Therapy

• Reserved for immunocompromised patients, complicated cases, and neonates 2, 5

Renal Impairment Adjustments

Dose reduction is mandatory in renal impairment to prevent acyclovir neurotoxicity, which can occur in up to 20% of patients without proper adjustment. 2, 3, 6

Oral Acyclovir Adjustments

Normal Dose	CrCl (mL/min/1.73m²)	Adjusted Dose	Interval
200 mg q4h	>10	200 mg	q4h
200 mg q4h	0-10	200 mg	q12h
400 mg q12h	>10	400 mg	q12h
400 mg q12h	0-10	200 mg	q12h
800 mg q4h	>25	800 mg	q4h
800 mg q4h	10-25	800 mg	q8h
800 mg q4h	0-10	800 mg	q12h

3

Hemodialysis

• Administer additional dose after each dialysis session 3
• Hemodialysis removes approximately 60% of acyclovir over 6 hours 6
• Recommended regimen: Loading dose 400 mg, maintenance 200 mg twice daily, with 400 mg post-dialysis 6

Peritoneal Dialysis

• No supplemental dose needed after interval adjustment 3

Critical Safety Considerations

Nephrotoxicity Prevention

• Maintain adequate hydration throughout therapy 2, 3
• Monitor renal function, especially after 4 days of IV therapy when reversible nephropathy typically manifests 2
• Risk affects up to 20% of patients receiving IV acyclovir 2
• Avoid concurrent nephrotoxic agents 3

Augmented Renal Clearance (ARC)

• Children with eGFR >250 mL/min/1.73m² may require higher IV doses (15-20 mg/kg every 6 hours) to achieve therapeutic concentrations 7
• Consider therapeutic drug monitoring in this population 7

Other Adverse Effects

• Rare: hepatitis, bone marrow failure, encephalopathy 2
• Neurotoxicity risk increases in dialysis patients without dose adjustment 6

Special Populations

Immunocompromised Patients

• Use IV acyclovir for varicella, disseminated VZV, and complicated HSV infections 2, 5
• Higher risk of acyclovir-resistant mutants with chronic infection 8

Neonates

• HSV encephalitis: 20 mg/kg IV every 8 hours for 21 days 1
• All neonatal herpes infections require IV therapy 5