Combined Intrathecal and Intramuscular Gentamicin for Gram-Negative Meningitis

Gentamicin concentrations in cerebrospinal fluid were studied in 21 adults treated with gentamicin and other antibiotics for proved or suspected meningitis due to gram-negative enteric bacilli. Sixteen patients were given three to 12 doses of 4 mg intrathecally. Within eight hours after an intrathecal injection in the lumbar area of 4 mg, 11 of 14 cerebrospinal-fluid samples contained 19 to 46 μg per milliliter; after 20 hours two thirds contained less than 3 μg per milliliter. The geometric mean half-life of gentamicin in cerebrospinal fluid was 5.5 hours. Intrathecal injections of 4 mg of gentamicin must be repeated at least every 18 hours to maintain therapeutic concentrations in lumbar cerebrospinal fluid despite concomitant intramuscular administration. (N Engl J Med 290:1394–1398, 1974)