What is the rationale for adding ampicillin to empiric meningitis therapy in patients aged ≥50 or immunocompromised?

• A. To cover Listeria monocytogenes, which commonly affects older adults and immunocompromised individuals.
• B. To enhance MRSA coverage.
• C. To cover anaerobes.
• D. To reduce potential drug interactions.

Answer: (D)

Older adults and immunocompromised patients are at risk for meningitis caused by Listeria monocytogenes, which cephalosporins alone often fail to cover. Ampicillin provides reliable activity against Listeria, so adding it to empiric meningitis therapy ensures this pathogen is treated from the start. In practice, the regimen for these high-risk groups includes a beta-lactam to cover common organisms plus ampicillin specifically to cover Listeria. The aim is not to boost MRSA or anaerobe coverage, and ampicillin isn’t used to reduce drug interactions. The key reason for including ampicillin is to cover Listeria monocytogenes.