Ceftriaxone, a new third-generation cephalosporin, appears to be promising for the therapy of acute bacterial meningitis. The 90% MBCs of ceftriaxone against 54 recent cerebrospinal fluid isolates of Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae were .0.06 to 0.25 j.Lg/ml. We examined the efficacy and safety of ceftriaxone therapy of meningitis in Bahia, Brazil. The study was conducted in two phases; in phase A, ceftriaxone was coadministered with ampicillin. The mean cerebrospinal fluid concentrations of ceftriaxone 24 h after an intravenous dose of 80 mg/kg were 4.2 and 2.3 ,ug/ml on days 4 to 6 and 10 to 12 of therapy, respectively. These concentrations were 8-to more than 100-fold greater than the 90% MBCs against the relevant pathogens. In phase B, ceftriaxone (administered once daily at a dose of 80 mg/kg after an initial dose of 100 mg/kg) was compared with conventional dosages of ampicillin and chloramphenicol in a prospective randomized trial of 36 children and adults with meningitis. The groups were comparable based on clinical, laboratory, and etiological parameters. Ceftriaxone given once daily produced results equivalent to those obtained with ampicillin plus chloramphenicol, as judged by cure rate, case fatality ratio, resolution with sequelae, type and severity of sequelae, time to sterility of cerebrospinal fluid, and potentially drug-related adverse effects. The cerebrospinal fluid bactericidal titers obtained 16 to 24 h after ceftriaxone dosing were usually 1:512 to >1:2,048 even late in the treatment course, compared with values of 1:8 to 1:32 in patients receiving ampicillin plus chloramphenicol. Ceftriaxone clearly deserves further evaluation for the therapy of meningitis; the optimal dose, dosing frequency (every 12 h or every 24 h), and duration of therapy remain to be determined.Bacterial meningitis remains a relatively common disease worldwide. The recent emergence of pneumococci resistant to penicillin or chloramphenicol or both (18,27), the emergence of Haemophilus influenzae strains resistant to ampicillin or chloramphenicol or both (16,32,44,45), the continued high mortality due to gram-negative bacillary meningitis despite therapy with aminoglycosides or chloramphenicol or both (7), and the potential toxicity of chloramphenicol have all prompted the search for alternative agents for the therapy of meningitis.Ceftriaxone (RO13-9904) is a new third-generation cephalosporin with excellent in vitro activity against all major meningeal pathogens (1, 14, 17, 28, 39; Scheld, Rocha, Sande, and Bryan, Am. J. Med., in press), except Listeria monocytogenes. In addition, ceftriaxone was the most rapidly bactericidal agent within the cerebrospinal fluid (CSF) in vivo when it was compared with moxalactam, cefotaxime, ampicillin, and netilmicin in experimental animal models of meningitis induced by Escherichia coli, Streptococcus agalactiae, Streptococcus pneumoniae, or H. influenzae (9,11,24,34; Scheld et al., in press). Although the ceftriaxone concentrations in CS...