Meropenem (MEPM), a novel parenteral carbapenem antibiotic, was examined in a cooperative study involving 12 pediatric and 1 neonatologic facilities. The results are summarized as follows. 1. Antibacterial activity Antibacterial activity of MEPM against stock organisms including 31 strains of Streptococcus agalactiae, 14 of Listeria monocytogenes, 4 of Bordetella pertussis and 3 of Neisseria meningitidis ranged from 0.025 to 0.10 micrograms/ml in MIC90's, which were equal or lower than those of control drugs such as imipenem cefazolin, cefotiam, cefotaxime, ceftazidime and latamoxef. MICs against clinical isolates were as follows: In Gram-positive bacteria, MICs were 0.20 micrograms/ml to 6.25 micrograms/ml against 3 strains of Staphylococcus aureus, and 0.025 micrograms/ml or less against 4 of Streptococcus pneumoniae. In Gram-negative bacilli, MICs were 0.10 micrograms/ml to 0.20 micrograms/ml against 3 strains of Haemophilus influenzae and 0.78, 0.10 and 0.78 micrograms/ml, respectively, against one strain each of Enterobacter cloacae, Morganella morganii and Pseudomonas aeruginosa. MIC against 1 strain of Peptococcus saccharolyticus was < or = 0.025 micrograms/ml. 2. Pharmacokinetics Maximum plasma concentrations after intravenous infusion of MEPM over 30 minutes at doses of 10, 20 and 40 mg/kg, respectively, to 3 different groups of 3 children (total 9 cases) were observed at the completion of the treatment. Mean maximum concentrations in the 3 groups were 36.3, 69.5 and 129.8 micrograms/ml, respectively, exhibiting clear dose response. Mean plasma half lives in beta phase were 0.94, 0.86 and 0.94 hours, respectively, exhibiting no difference by doses, and this trend was observed also by HPLC. Urinary excretion rates in the first 6 hours after dose in the 10, 20 and 40 mg/kg groups were 67.3, 65.6 and 68.4%, respectively. Concentrations of MEPM in cerebrospinal fluid were determined in 2 cases of pyogenic meningitis. In 1 case, 500 mg (5.9 mg/kg) of MEPM was infused intravenously over 30 minutes and concentrations on Days 6, 8 and 15 observed at 190, 60 and 100 minutes after respective doses were 0.13, 0.10 micrograms/ml and less than the detection limit. Cerebrospinal fluid-plasma concentration ratio was determinable only on Day 8 and was 2.8%. In another case to which 250 mg (38.5 mg/kg) of MEPM was infused intravenously over 30 minutes, the concentration at Days 6, 7 and 10, 1 hour after the dose were less than the detection limit on day 6, and 2.04 and 2.62 micrograms/ml, respectively on days 7 and 10. 3. Clinical efficacy Clinical efficacies were evaluated in 49 cases and the efficacy rate was 93.9%.(ABSTRACT TRUNCATED AT 400 WORDS)