Acyclovir Dosing for HSV Meningitis
For adults with HSV meningitis and normal renal function, administer acyclovir 10 mg/kg intravenously every 8 hours for 14-21 days. 1, 2
Standard Dosing Protocol
- The dose is 10 mg/kg IV every 8 hours (total daily dose of 30 mg/kg/day) for adults with confirmed or suspected HSV meningitis 1, 2, 3
- Each dose should be infused over 1 hour to minimize nephrotoxicity 4
- Treatment duration should be 14-21 days to ensure adequate viral suppression and prevent relapse 1, 3
Critical Distinction: Meningitis vs. Encephalitis
While the question asks about meningitis, it's essential to recognize that HSV encephalitis requires the same dose (10 mg/kg IV every 8 hours) but represents a more severe condition with altered mental status and parenchymal brain involvement 1, 2. The dosing is identical, but the clinical urgency differs—encephalitis has mortality rates of 70% without treatment versus 20-30% with acyclovir 5.
Treatment Initiation and Monitoring
- Start acyclovir within 6 hours of admission if HSV CNS infection is suspected, even before CSF PCR confirmation, as early treatment (within 4 days of symptom onset) reduces mortality to 8% compared to 28% with delayed treatment 1, 2
- CSF PCR remains positive for 7-10 days after starting treatment, so delayed lumbar puncture can still confirm diagnosis 5
- Consider repeat CSF PCR at 14-21 days in patients without appropriate clinical response; if still positive, continue antiviral therapy 1, 2
Hydration and Nephrotoxicity Prevention
- Maintain adequate hydration throughout treatment as acyclovir can cause crystalluria and obstructive nephropathy in up to 20% of patients, typically manifesting after 4 days of IV therapy 5, 1
- Monitor serum creatinine regularly during treatment 1, 4
- The drug is 62-91% renally excreted, making renal function monitoring mandatory 4
Common Pitfalls to Avoid
- Never use oral acyclovir for acute HSV meningitis—IV therapy is mandatory for CNS infections as oral formulations do not achieve adequate CSF levels 5
- Do not use fixed doses; always calculate based on actual body weight at 10 mg/kg 2
- Do not stop treatment prematurely—the original 10-day regimens led to relapse rates of 26-29% in children, which is why current guidelines recommend 14-21 days 5
Renal Dose Adjustments
For patients with impaired renal function, dose adjustments are mandatory 1, 4:
- Creatinine clearance >50 mL/min: Standard dose (10 mg/kg every 8 hours)
- Creatinine clearance 25-50 mL/min: 10 mg/kg every 12 hours
- Creatinine clearance 10-25 mL/min: 10 mg/kg every 24 hours
- Hemodialysis patients: 5 mg/kg after each dialysis session 4
Special Populations
Immunocompromised Patients
- May require prolonged courses beyond 21 days if CSF PCR remains positive 5, 1
- If acyclovir resistance is suspected (persistent symptoms despite therapy), consider foscarnet 40 mg/kg IV every 8 hours as alternative 5, 6
Pediatric Dosing
- Children 3 months to 12 years: 500 mg/m² IV every 8 hours (equivalent to approximately 20 mg/kg/day) 1, 7
- Neonates with HSV CNS disease: 20 mg/kg IV every 8 hours for 21 days (higher dose due to worse outcomes in this age group) 5, 2
- Adolescents >12 years: Adult dosing of 10 mg/kg IV every 8 hours 1
Relapse Considerations
- Relapse rates can reach 5% even after appropriate treatment, particularly in children aged 3 months-12 years (up to 29%) 5, 1
- Patients with recurrent HSV-2 meningitis may benefit from suppressive therapy with oral valacyclovir after the acute episode, though optimal duration is not well-established 8