What is the recommended treatment for Herpes Simplex Virus (HSV) encephalitis?

Treatment of Herpes Simplex Virus (HSV) Encephalitis

Intravenous aciclovir at a dose of 10 mg/kg every 8 hours for 14-21 days is the recommended treatment for HSV encephalitis. 1

Initial Management

• Treatment should be initiated as soon as HSV encephalitis is suspected, ideally within 6 hours of admission
• Do not wait for confirmatory test results if clinical suspicion is high
• Early treatment significantly improves outcomes - mortality decreases to 8% if therapy is initiated within 4 days of symptom onset 1

Dosing Recommendations:

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

Duration of Treatment:

• 14-21 days of intravenous aciclovir is recommended for confirmed cases 1
• For children aged 3 months-12 years, a minimum of 21 days is recommended due to higher relapse rates in this age group 1

Monitoring During Treatment

• Monitor renal function regularly, especially after 4 days of therapy when nephropathy risk increases
• Maintain adequate hydration to reduce risk of crystalluria and obstructive nephropathy
• Adjust dosage in patients with pre-existing renal impairment 1

Follow-up Testing

• A repeat lumbar puncture with HSV PCR testing should be performed at the end of treatment (14-21 days) 1
• If CSF remains positive for HSV by PCR, continue aciclovir treatment with weekly CSF PCR until negative 1

When to Stop Empirical Treatment

Aciclovir can be discontinued in immunocompetent patients if:

• An alternative diagnosis has been established, OR
• HSV PCR in CSF is negative on two occasions 24-48 hours apart AND MRI is not characteristic for HSV encephalitis, OR
• HSV PCR in CSF is negative once >72 hours after symptom onset, with normal level of consciousness, normal MRI (performed >72 hours after symptom onset), and CSF white cell count <5 × 10⁶/L 1

Prognostic Factors

Poor prognostic factors include:

• Age >30 years
• Low Glasgow Coma Score (<6)
• Treatment delay >48 hours after admission
• Simplified Acute Physiology Score >27 at hospital admission 1

Important Considerations

• Oral aciclovir does not achieve adequate CSF levels and should not be used for HSV encephalitis 1
• Valaciclovir has occasionally been used after initial IV aciclovir treatment when maintaining IV access is difficult, but is not licensed for this indication in children 1
• Relapse rates as high as 5% in adults and 26-29% in children have been reported, particularly with treatment courses <14 days 1
• Recent research suggests that for patients <79 kg, a minimum dosage of 2550 mg/day (850 mg/8 hours) may improve outcomes 2

Adjunctive Therapy

• There is limited evidence for the use of adjunctive corticosteroids in HSV encephalitis
• One non-randomized retrospective study suggested potential benefit, but further research is needed before this can be recommended 1