Cefotaxime and ceftriaxone have proven to be effective in pyogenic infections of the central nervous system. Since in some bacterial central nervous system infections the blood-cerebrospinal fluid (CSF) barrier is either minimally impaired or recovers in the course of the illness, we studied the penetration of both antibiotics in the absence of inflamed meninges. Patients who had undergone external ventriculostomies for noninflammatory occlusive hydrocephalus received either cefotaxime (2 g/30 min) or ceftriaxone (2 g/30 min) to treat extracerebral infections. Serum and CSF were drawn repeatedly after the first dose. With ceftriaxone, they were also drawn after the last dose. The concentrations of cefotaxime, its metabolite desacetylcefotaxime, and ceftriaxone were determined by high-performance liquid chromatography with UV detection. Maximum concentrations of cefotaxime in CSF were reached 0.5 to 8 h (median = 3 h; n = 6) after the end of the infusion and ranged from 0.14 to 1.81 mg/liter (median = 0.44 mg/liter; n = 6). Maximum levels of ceftriaxone in CSF ranging from 0.18 to 1.04 mg/liter (median = 0.43 mg/liter; n = 5) were seen 1 to 16 h (median = 12 h; n = 5) after the infusion. The elimination half-life of cefotaxime in CSF was 5.0 to 26.9 h (median = 9.3 h; n = 5), and that of ceftriaxone was 15.7 to 18.4 h (median = 16.8 h; n = 3). It is concluded that after a single dose of 2 g, maximal concentrations of cefotaxime and ceftriaxone in CSF do not differ substantially. The long elimination half-lives guarantee uniform concentrations in CSF. These concentrations reliably inhibit highly susceptible bacteria but cannot be relied on to inhibit staphylococci and penicillin G-resistant Streptococcus pneumoniae.Because of its morbidity and lethality, bacterial meningitis remains a major medical concern throughout the world. The emergence of bacteria not susceptible to standard antibacterial agents in meningitis of children and immunocompromised adults has stimulated the search for alternative drugs. Broad-spectrum cephalosporins have a broad range of in vitro antibacterial activities, including that against most organisms responsible for purulent meningitis (6,7,19), and have been successfully applied as single agents for this indication in children and adults (3,9,29,34,37 Two grams of cefotaxime (Claforan; Hoechst AG, Frankfurt/M, Germany) or 2 g of ceftriaxone (Rocephin; Hoffmann-La Roche, Grenzach-Wyhlen, Germany) was infused intravenously within 30 min. Single-dose pharmacokinetics were determined after the first infusion for six patients receiving cefotaxime and six patients receiving ceftriaxone. To obtain a 24-h time course with cefotaxime, the second infusion was administered 24 h after the first dose. Thereafter, therapy was continued with 2 g three times a day or twice a day. For this reason, patients with pneumonia or fever greater than 38.5°C during the 24-h interval before the