This patient should begin empiric antibiotic treatment with intravenous penicillin and metronidazole. She has severe, unremitting headache and focal neurologic findings, both indicating a presumed brain abscess with an odontogenic source. Abscesses resulting from dental sepsis are usually caused by mixed Fusobacterium, Prevotella, and Bacteroides species and by streptococci. Penicillin covers most mouth flora, including both aerobic and anaerobic streptococci, and metronidazole provides additional anaerobic coverage with excellent tissue penetration.

Meropenem would be an appropriate antibiotic choice if there was concern about Pseudomonas aeruginosa infection, which would be more common in a brain abscess involving neurosurgical procedures. However, P. aeruginosa is not a typical source of brain abscess resulting from an odontogenic focus.

Trimethoprim-sulfamethoxazole and vancomycin would provide inadequate coverage against the pathogens typically found in brain abscesses with an odontogenic source. Intravenous vancomycin and a third-generation cephalosporin would be most appropriate for management of brain abscess related to neurosurgery or trauma. This patient's brain abscess is from an odontogenic source, so treatment with penicillin and metronidazole is most appropriate.