Empirical therapy for encephalitis

Britton 2015

Start aciclovir therapy in all patients with suspected acute encephalitis while further investigations are underway, because herpes simplex virus (HSV) is the most common treatable cause.

In adults and children 1 month and older with suspected acute encephalitis, use:

aciclovir intravenously, 8-hourlyaciclovir aciclovir aciclovir

adult and child older than 12 years: 10 mg/kg¹. For dosage adjustment in adults with kidney impairment, see aciclovir intravenous dosage adjustment

child younger than 5 years: 20 mg/kg or 500 mg/m²² ³

child 5 years to 12 years: 15 mg/kg or 500 mg/m²² ³.

Add treatment with antibiotics for patients with suspected acute encephalitis in whom bacterial meningitis or sepsis is possible – see Meningitis in adults and children 2 months or older or Meningitis in neonates and children younger than 2 months.

For management of neonates with suspected herpes simplex infection, see Neonatal herpes simplex infection.

Note: If bacterial meningitis or sepsis is possible, empirical antibiotics are required.

Herpes simplex encephalitis can usually be excluded and empirical therapy stopped based on negative CSF nucleic acid amplification test results (eg polymerase chain reaction [PCR]) and a normal MRI. However, test results for HSV in CSF can be negative in very early disease (before day 3 of illness); consider a repeat lumbar puncture and PCR if clinical suspicion is high.

Add empirical therapy for Listeria monocytogenes infection for patients at risk; this includes patients who:

are older than 50 years
are younger than 1 month (ie neonates)
have immune compromise
are pregnant
have a history of hazardous alcohol consumption.

For adults, add to aciclovir:

benzylpenicillin 2.4 g intravenously, 4-hourly. For dosage adjustment in adults with kidney impairment, see benzylpenicillin dosage adjustment.benzylpenicillin benzylpenicillin benzylpenicillin

Benzylpenicillin is the preferred drug for Listeria infection because L. monocytogenes is intrinsically resistant to cephalosporins. However, benzylpenicillin may not be appropriate for patients who have penicillin hypersensitivity. For adults who report penicillin hypersensitivity, carefully assess the nature and severity of the reaction (see Principles of assessment of adults reporting antimicrobial hypersensitivity), and consider whether use of benzylpenicillin is precluded. If benzylpenicillin is not used, for adults, add:

trimethoprim+sulfamethoxazole 5+25 mg/kg up to 480+2400 mg intravenously, 6-hourly. For dosage adjustment in adults with kidney impairment, see trimethoprim+sulfamethoxazole dosage adjustment.trimethoprim + sulfamethoxazole trimethoprim+sulfamethoxazole trimethoprim+sulfamethoxazole

For management of neonates and children with possible L. monocytogenes infection, seek expert advice.

When the diagnosis is confirmed and a pathogen has been identified, modify treatment accordingly. Advice on directed therapy is included in these guidelines for:

If no pathogen is identified, seek specialist advice for further investigation and management (including consideration of antibody testing and immunotherapy for possible immune-mediated causes).

¹ Aciclovir dosing in obesity is poorly defined; however, limited data support dosing based on adjusted body weight in adults and ideal body weight in children. For simplicity, some centres recommend a maximum dosing weight of 100 kg (eg 1 g for 10 mg/kg doses, 1.5 g for 15 mg/kg doses).Return

² Use the online calculator to determine body surface area.Return

³ Aciclovir dosing in obesity is poorly defined; however, limited data support dosing based on ideal body weight in children.Return