What is the recommended dose of Aciclovir (acyclovir) for the treatment of meningoencephalitis?

Aciclovir Dosing for Meningoencephalitis

For herpetic meningoencephalitis, the recommended dose of intravenous aciclovir is 10 mg/kg every 8 hours for adults and children >12 years, and 500 mg/m² every 8 hours for children 3 months-12 years. 1

Age-Specific Dosing

• Adults and children >12 years: 10 mg/kg IV every 8 hours 2, 1
• Children 3 months-12 years: 500 mg/m² IV every 8 hours 2, 1
• Neonates: 20 mg/kg IV every 8 hours 1

Duration of Treatment

• HSV encephalitis: 14-21 days 1
• Children: Minimum of 21 days recommended due to higher relapse rates 1
• HSV meningitis: 10-14 days, with shorter courses sometimes used for recurrent HSV-2 meningitis 2, 3

Important Considerations

Renal Function

• Dose adjustment is required in patients with pre-existing renal impairment 2, 1, 4
• Monitor renal function regularly, especially after 4 days of therapy when nephropathy risk increases 1, 4
• Maintain adequate hydration to prevent crystalluria and obstructive nephropathy 2, 4

Administration

• Must be administered by intravenous infusion, not bolus injection 4
• Oral aciclovir should not be used for meningoencephalitis due to poor CNS penetration 1

Timing of Treatment

• Treatment should be started immediately upon suspicion of herpetic encephalitis 2, 1
• For suspected encephalitis, start aciclovir within 6 hours of admission 2
• Early initiation significantly improves outcomes, reducing mortality from >70% to <30% 1

Diagnostic Considerations

• Do not delay treatment while waiting for diagnostic confirmation 1
• Lumbar puncture for CSF analysis including HSV PCR should be performed 1
• Even if aciclovir has been started, CSF PCR remains positive for 7-10 days 2

Monitoring During Treatment

• Regular assessment of:
  • Renal function (serum creatinine, BUN, creatinine clearance) 1, 4
  • Neurological status 1
  • Fluid balance 2, 4

When to Consider Stopping Treatment

• Aciclovir can be stopped if:
  • An alternative diagnosis has been confirmed
  • HSV PCR in CSF is negative on two occasions 24-48 hours apart and MRI is not characteristic for HSV encephalitis
  • HSV PCR in CSF is negative once >72 hours after symptom onset with unaltered consciousness, normal MRI, and CSF white cell count <5 × 10^6/L 1

Common Pitfalls to Avoid

• Delaying treatment while waiting for diagnostic confirmation 1
• Administering incorrect aciclovir dosage 1
• Stopping treatment based on a single negative CSF PCR 1
• Using oral aciclovir instead of IV formulation 1
• Inadequate hydration leading to renal toxicity 2, 4
• Premature cessation of therapy before completing the recommended course 1

Remember that HSV encephalitis is a medical emergency with high mortality if left untreated, and treatment outcomes are significantly improved with prompt initiation of appropriate aciclovir dosing.