What empiric antibiotics, doses, and treatment duration are recommended for bacterial meningitis in adults (18‑50 years), older adults, immunocompromised patients, neonates, children, and in patients with severe beta‑lactam allergy or penicillin allergy?

Empiric Antibiotics for Bacterial Meningitis

Antibiotic therapy must be initiated within 1 hour of hospital presentation for suspected bacterial meningitis, as delayed treatment is strongly associated with increased mortality and poor neurological outcomes. 1

Critical Timing Principles

• Start antibiotics immediately upon clinical suspicion—do not wait for lumbar puncture or imaging. 1
• Obtain blood cultures before antibiotics, but never delay treatment beyond 1 hour to do so. 1, 2
• If lumbar puncture is delayed for any reason (CT scan, coagulopathy), empiric treatment must begin immediately. 1

Empiric Antibiotic Regimens by Population

Adults 18-50 Years (Immunocompetent)

Standard regimen:

• Ceftriaxone 2g IV every 12 hours (or 4g IV every 24 hours) 1
  • Alternative: Cefotaxime 2g IV every 4-6 hours 1
• PLUS Vancomycin 10-20 mg/kg IV every 8-12 hours (target trough 15-20 μg/mL) 1
  • Alternative to vancomycin: Rifampicin 300mg IV/PO every 12 hours 1

Rationale: This covers Streptococcus pneumoniae (including resistant strains) and Neisseria meningitidis, the most common pathogens in this age group. 1

Adults >50 Years OR Immunocompromised (Any Age)

Enhanced regimen:

• Ceftriaxone 2g IV every 12 hours (or 4g IV every 24 hours) 1
  • Alternative: Cefotaxime 2g IV every 4-6 hours 1
• PLUS Vancomycin 10-20 mg/kg IV every 8-12 hours (target trough 15-20 μg/mL) 1
• PLUS Ampicillin 2g IV every 4 hours (or amoxicillin 2g IV every 4 hours) 1

Rationale: The addition of ampicillin provides coverage for Listeria monocytogenes, which occurs in patients >50 years, diabetics, those on immunosuppressive drugs, cancer patients, and other immunocompromising conditions. 1

Children 1 Month to 18 Years

Pediatric regimen:

• Ceftriaxone 50 mg/kg IV every 12 hours (maximum 2g every 12 hours) 1
  • Alternative: Cefotaxime 75 mg/kg IV every 6-8 hours 1
• PLUS Vancomycin 10-15 mg/kg IV every 6 hours (target trough 15-20 μg/mL) 1
  • Alternative to vancomycin: Rifampicin 10 mg/kg every 12 hours (maximum 600mg/day) 1

Neonates <1 Month

Neonatal regimen varies by age:

Age <1 week:

• Ampicillin 50 mg/kg IV every 8 hours 1
• PLUS Cefotaxime 50 mg/kg IV every 8 hours 1
  • Alternative to cefotaxime: Gentamicin 2.5 mg/kg IV every 12 hours 1

Age 1-4 weeks:

• Ampicillin 50 mg/kg IV every 6 hours 1
• PLUS Cefotaxime 50 mg/kg IV every 6-8 hours 1
  • Alternative aminoglycosides: Gentamicin 2.5 mg/kg IV every 8 hours, tobramycin 2.5 mg/kg IV every 8 hours, or amikacin 10 mg/kg IV every 8 hours 1

Rationale: Neonatal meningitis has a different pathogen spectrum including Group B Streptococcus, E. coli, and Listeria monocytogenes. 1

Severe Beta-Lactam/Penicillin Allergy

For patients with anaphylaxis history to beta-lactams:

• Chloramphenicol 25 mg/kg IV every 6 hours 3
• PLUS Vancomycin 10-20 mg/kg IV every 8-12 hours (target trough 15-20 μg/mL) 3
• PLUS Trimethoprim-sulfamethoxazole (for Listeria coverage if indicated by age/risk factors) 3

Important caveat: True anaphylactic reactions to cephalosporins are rare even in penicillin-allergic patients. Consider infectious disease consultation urgently, as alternative regimens have less robust CNS penetration. 3

Treatment Duration by Pathogen

Once pathogen is identified, adjust duration accordingly:

• Neisseria meningitidis: 5-7 days total 2, 3, 4
• Streptococcus pneumoniae: 10-14 days total 2, 3, 4
• Haemophilus influenzae: 10 days total 2, 3
• Listeria monocytogenes: 21 days total 2, 3, 4
• Gram-negative bacilli (Enterobacteriaceae): 21 days total 3
• Culture-negative (no pathogen identified): 10 days total if clinically recovered 2

Adjunctive Dexamethasone Therapy

• Dexamethasone 10mg IV every 6 hours for adults (0.15 mg/kg every 6 hours for children) should be given immediately before or with the first antibiotic dose. 2, 4, 5
• Continue for 4 days if pneumococcal meningitis is confirmed or probable. 4
• This reduces mortality and neurological morbidity specifically in pneumococcal meningitis. 4, 5

Common Pitfalls to Avoid

• Never delay antibiotics for imaging. If CT is indicated (focal deficits, new seizures, GCS <10, severely immunocompromised), start antibiotics first, then image. 1
• Do not omit ampicillin in patients >50 years or immunocompromised. Listeria coverage is critical in these populations, and cephalosporins have no activity against this pathogen. 1
• Do not underdose antibiotics. Meningitis requires high-dose therapy to achieve adequate CSF penetration—using standard dosing will result in treatment failure. 1
• Do not stop antibiotics when fever resolves. Clinical improvement does not equal microbiological cure; complete the pathogen-specific duration. 2
• Do not forget blood cultures before antibiotics. While treatment should not be delayed, blood cultures provide critical diagnostic information. 1, 2

Regional Resistance Considerations

• In areas with high pneumococcal penicillin resistance or after recent travel to such regions, vancomycin or rifampicin must be added to the cephalosporin. 1, 3
• Some experts suggest ceftriaxone/cefotaxime alone may suffice when true resistance to third-generation cephalosporins (MIC >2 mg/L) is not expected, but this is controversial—err on the side of adding vancomycin. 1