In community-acquired bacterial meningitis, what is the usual empiric antibiotic regimen for adults 18-50 and for adults over 50 or with risk factors?

• A. 18-50: vancomycin + ceftriaxone ± dexamethasone; over 50: add ampicillin
• B. 18-50: vancomycin + ceftriaxone ± dexamethasone; over 50: add metronidazole
• C. 18-50: vancomycin alone
• D. 18-50: dexamethasone alone

Answer: (B)

Empiric therapy for community-acquired bacterial meningitis must rapidly cover the pathogens most likely to cause disease, with a crucial adjustment for age because Listeria monocytogenes becomes a concern in older adults. For adults up to 50, the typical approach is vancomycin plus a third-generation cephalosporin (like ceftriaxone) to cover penicillin-resistant pneumococcus, Neisseria meningitidis, and other common bacteria, with dexamethasone given around the first antibiotic dose to lessen inflammatory damage. If the patient is over 50 or has risk factors, ampicillin is added to cover Listeria. Metronidazole isn’t part of the standard initial regimen for this scenario, and vancomycin or dexamethasone alone wouldn’t provide adequate coverage.