What bacteria should be covered in empiric antibiotic therapy for suspected bacterial meningitis?

Empiric Antibiotic Coverage for Suspected Bacterial Meningitis

Empiric antibiotic therapy for suspected bacterial meningitis should include a third-generation cephalosporin (ceftriaxone or cefotaxime) plus vancomycin, with additional ampicillin/amoxicillin for patients over 60 years or immunocompromised to cover Listeria. 1, 2

Core Pathogens to Cover

The most common bacterial pathogens causing meningitis that require empiric coverage include:

• Streptococcus pneumoniae (43% of cases) 1
• Neisseria meningitidis (16% of cases) 1
• Listeria monocytogenes (8% of cases, especially in older adults) 1
• Haemophilus influenzae (less common since vaccination) 2

Age-Based Empiric Regimens

Adults <60 years:

• First-line: Ceftriaxone 2g IV q12h OR Cefotaxime 2g IV q6h
• PLUS: Vancomycin 15-20 mg/kg IV q8-12h (to achieve serum trough concentrations of 15-20 μg/mL) 1, 2

Adults ≥60 years or Immunocompromised:

• First-line: Ceftriaxone 2g IV q12h OR Cefotaxime 2g IV q6h
• PLUS: Vancomycin 15-20 mg/kg IV q8-12h
• PLUS: Ampicillin/Amoxicillin 2g IV q4h (for Listeria coverage) 1, 2

Special Considerations

• Recent travel: If the patient has traveled within the past 6 months to a country with high rates of penicillin-resistant pneumococci, add vancomycin (if not already included) or rifampicin 600mg IV/PO q12h 1

• Penicillin allergy: If there is a clear history of anaphylaxis to penicillins or cephalosporins, use chloramphenicol 25 mg/kg IV q6h 1

• Immunocompromised patients: Include ampicillin/amoxicillin for Listeria coverage (this includes patients with diabetes and history of alcohol misuse) 1

Timing of Administration

Time from hospital entry to antibiotic administration should not exceed 1 hour 2. If lumbar puncture is delayed due to need for neuroimaging, start empiric antibiotics before the procedure.

Duration of Therapy

• S. pneumoniae: 10-14 days
• N. meningitidis: 7 days
• Staphylococcal meningitis: at least 14 days
• Culture-negative cases: at least 14 days 2

Adjusting Therapy Based on Culture Results

Once culture and susceptibility results are available, therapy should be modified accordingly:

• Penicillin-sensitive pathogens: Continue ceftriaxone/cefotaxime or switch to benzylpenicillin
• Penicillin-resistant pathogens: Add vancomycin and rifampicin if not already included
• Resistant to both penicillin and cephalosporin: Continue triple therapy with ceftriaxone/cefotaxime plus vancomycin plus rifampicin 2

Common Pitfalls to Avoid

1. Failing to cover Listeria in patients ≥60 years or immunocompromised
2. Not adding vancomycin when pneumococcal resistance is suspected
3. Delaying antibiotic administration while waiting for diagnostic procedures
4. Stopping antibiotics too early before completing the recommended duration
5. Not adjusting therapy based on culture results and susceptibility patterns 2

Adjunctive Therapy

Dexamethasone 10mg IV q6h for 4 days, starting before or with the first antibiotic dose, should be considered, particularly when S. pneumoniae is suspected 2.

Remember that prompt administration of appropriate empiric antibiotics is critical for reducing mortality and morbidity in bacterial meningitis. The regimen should be started immediately when meningitis is suspected, even before confirmatory tests are complete.