Ceftazidime (CAZ) was administered to 34 full-term and premature infants aged 0-27 days with various bacterial infections in a dose of 10 or 20 mg/kg by intravenous bolus injection, and plasma concentrations and urinary recovery rates in these subjects during recovery periods were studied. Because of the small number of the cases recruited, neonates were not divided into the full-term and the premature group, but into 3 groups based on day-age: 0-3 days, 4-7 days, and 8 days or older. Concentrations and rates of transfer of CAZ into cerebrospinal fluid (CSF) were determined in 2 cases, and biliary concentrations in another case. A clinical evaluation of CAZ was performed in 12 male and 6 female infants aged 1 day to 4 months and 19 days, including 2 each with purulent meningitis, pneumonia and pyelonephritis, 3 with septicemia, 1 each with septicemia suspected, cholangitis, osteomyelitis, bronchopneumonia, staphylococcal scaled skin syndrome, and acute enterocolitis and 3 for prophylactic use. Plasma concentrations and urinary recovery rates of CAZ The intravenous bolus injection at 10 mg/kg. Peak plasma concentrations of CAZ were obtained at the first collection (30 minutes) of blood samples or 1 hour in all 3 groups, ranging from 23.3 to 26.9 micrograms/ml with no significant variations, plasma concentrations then slowly decreased, and were still 6.04-9.88 micrograms/ml even at 6 hours after the administration. The half-lives of CAZ in plasma tended to be shorter in older day-age neonates, with mean half-lives being 3.59, 2.50 and 2.50 hours for the youngest. The intravenous bolus injection at 20 mg/kg. Peak concentrations were obtained at the first collection of blood samples in all 3 groups (0-3 days: 15 minutes, the others: 30 minutes), being 54.8, 39.9 and 43.8 micrograms/ml, respectively, then slowly decreased and were still 10.4-15.7 micrograms/ml even at 6 hours after the administration. Inter-age differences in half-lives were marked, i.e., 3.6 hours in 0-3-day group, 3.48 hours in 4-7-day group and 2.75 hours in 8-day or older group. Urinary recovery rates were about 40-60% without reference to day-age neonates. CSF concentrations About 50 mg/kg of CAZ was given to each of 2 cases.(ABSTRACT TRUNCATED AT 400 WORDS)