What is the maximum recommended daily dose of Acyclovir (antiviral medication) for treating meningitis?

Maximum Daily Dose of Acyclovir for Meningitis

The maximum daily dose of acyclovir for HSV meningitis in adults is 30 mg/kg/day (10 mg/kg IV every 8 hours), which totals approximately 2,100 mg/day for a 70 kg patient. 1

Adult Dosing

• Standard dose: 10 mg/kg IV every 8 hours for 14-21 days in adults with normal renal function 1
• This translates to 30 mg/kg/day as the maximum total daily dose 1
• Treatment duration should be 14-21 days to ensure adequate viral suppression and prevent relapse 1

Pediatric Dosing

The dosing differs significantly by age group:

• Children 3 months-12 years: 500 mg/m² IV every 8 hours (maximum 1,500 mg/m²/day) 2, 1
• Adolescents >12 years: 10 mg/kg IV every 8 hours (maximum 30 mg/kg/day) 2, 1
• Neonates require higher doses: 20 mg/kg IV every 8 hours for 21 days (maximum 60 mg/kg/day), which has shown improved outcomes with decreased mortality to 5% 1

Critical Distinction: Meningitis vs. Encephalitis

HSV meningitis requires lower doses and shorter duration than encephalitis - this is a crucial clinical distinction:

• Meningitis is characterized by meningeal signs and CSF pleocitosis without altered mental status 1
• Encephalitis involves altered mental status, focal neurological deficits, and parenchymal brain involvement requiring more aggressive treatment 1
• The guidelines primarily address encephalitis dosing, but these translate to meningitis management 1

Mandatory Dose Adjustments

Reduce dosing in renal impairment - acyclovir is 62-91% renally excreted:

• Dose must be adjusted based on creatinine clearance to prevent crystalluria and obstructive nephropathy 1
• Calculate dose based on ideal body weight for height, not actual weight in obese or overweight patients to avoid excessive dosage and toxicity 3
• Even non-obese, overweight patients are at risk when actual body weight is used instead of ideal body weight 3

Monitoring Requirements

Monitor renal function throughout treatment to prevent nephrotoxicity:

• Nephrotoxicity manifests after 4 days of IV therapy in up to 20% of patients 1
• Maintain adequate hydration to reduce nephrotoxicity risk 1
• Rare adverse events include hepatitis, bone marrow suppression, and encephalopathy 1
• Monitor for neurotoxicity, particularly in patients with renal impairment or those receiving excessive doses 3

Common Pitfalls to Avoid

• Never use oral acyclovir for acute viral meningitis requiring hospitalization - IV therapy is mandatory for severe cases 1
• Do not dose based on actual body weight in overweight/obese patients - use ideal body weight to prevent toxicity 3
• Do not delay treatment beyond 6 hours if clinical suspicion is high, even if initial CSF or imaging is normal 2
• Do not assume valacyclovir suppressive therapy prevents recurrent HSV-2 meningitis - trials showed 500 mg twice daily did not prevent recurrent episodes 1

Treatment Response Monitoring

• Consider repeat CSF PCR at end of therapy in patients without appropriate clinical response 1
• If PCR remains positive for HSV at treatment completion, continue antiviral therapy 1
• Relapse rates can be as high as 5% after completion of acyclovir therapy 1