Empirical Antibiotic Regimens for Meningitis
All adults with suspected bacterial meningitis should immediately receive ceftriaxone 2g IV every 12 hours (or cefotaxime 2g IV every 6 hours) as the cornerstone of empirical therapy, with additional agents added based on age, immune status, and travel history. 1
Core Empirical Regimen by Patient Population
Adults <60 Years (Immunocompetent)
- Ceftriaxone 2g IV every 12 hours OR cefotaxime 2g IV every 6 hours 1
- This provides coverage for Streptococcus pneumoniae and Neisseria meningitidis, the most common pathogens in this age group 1
Adults ≥60 Years
- Ceftriaxone 2g IV every 12 hours OR cefotaxime 2g IV every 6 hours 1
- PLUS ampicillin 2g IV every 4 hours 1
- The addition of ampicillin is critical for Listeria monocytogenes coverage, which becomes increasingly prevalent in older adults 1
Immunocompromised Patients
- Ceftriaxone 2g IV every 12 hours OR cefotaxime 2g IV every 6 hours 1
- PLUS ampicillin 2g IV every 4 hours 1
- This includes patients with diabetes, alcohol misuse, cancer, or on immunosuppressive drugs 1
Additional Coverage for Special Circumstances
Recent Travel to Areas with Penicillin-Resistant Pneumococci
- ADD vancomycin 15-20 mg/kg IV every 12 hours 1
- OR rifampicin 600mg IV/PO every 12 hours 1
- This applies if the patient has been to a high-resistance area within the last 6 months 1
- The combination of ceftriaxone plus vancomycin has demonstrated synergistic activity against highly resistant pneumococcal strains 2, 3
Severe Penicillin/Cephalosporin Allergy
- Chloramphenicol 25 mg/kg IV every 6 hours 1
- PLUS co-trimoxazole 10-20 mg/kg (of trimethoprim component) in four divided doses (for patients ≥60 years or immunocompromised) 1
- This applies only to patients with a clear history of anaphylaxis 1
Critical Timing Considerations
- Antibiotics must be administered within 1 hour of hospital presentation 4, 5
- Blood cultures must be obtained before antibiotics, but should never delay treatment 4, 5
- If lumbar puncture is delayed for any reason (CT scan, coagulopathy correction), antibiotics must be given immediately 4, 5
- Delay in treatment is strongly associated with increased mortality and poor neurological outcomes 5
Rationale for Third-Generation Cephalosporins
Third-generation cephalosporins are the empirical antibiotic of choice because they have known bactericidal activity against both pneumococci and meningococci and penetrate inflamed meninges effectively 1. Although meningococci with reduced susceptibility to penicillin have been reported, patients infected by these strains respond to the high doses of penicillin or cephalosporins typically used in meningitis 1.
Common Pitfalls to Avoid
- Delaying antibiotics while waiting for imaging or lumbar puncture - antibiotics should be given within 1 hour even if diagnostic procedures are pending 4, 5
- Inadequate coverage for Listeria in patients ≥60 years or immunocompromised - always add ampicillin in these populations 1, 5
- Failing to obtain blood cultures before starting antibiotics - this is essential for pathogen identification and surveillance 4, 5
- Not considering local resistance patterns - especially after recent travel to areas with high pneumococcal resistance 1, 5
- Using calcium-containing solutions with ceftriaxone - do not use diluents containing calcium or administer simultaneously with calcium-containing IV solutions 6
Definitive Therapy Based on Culture Results
Streptococcus pneumoniae
- Continue ceftriaxone 2g IV every 12 hours or cefotaxime 2g IV every 6 hours for 10-14 days 1, 7, 5
- If penicillin-sensitive (MIC ≤0.06 mg/L), may switch to benzylpenicillin 2.4g IV every 4 hours 1, 5
- Recent evidence suggests that once-daily ceftriaxone 2g may be as effective as twice-daily dosing for highly susceptible strains, though twice-daily remains standard 8