Fundamental and clinical studies were carried out on imipenem/cilastatin sodium (MK-0787/MK-0791) in pediatric patients. The following results were obtained. A total of 238 clinical isolates stocked by our department was employed to determine the minimum inhibitory concentrations (MICs) of MK-0787 against various species of bacteria. The MK-0787 showed strong antibacterial activities against E. coli, Salmonella, Klebsiella, Proteus, Serratia, E. faecalis and S. epidermidis. Somewhat weaker activities were observed against P. aeruginosa and S. aureus. The MK-0787/MK-0791 was drip-infused intravenously into patients over a period of 1 hour, and serum levels of MK-0787 and MK-0791 were determined. At the dose level of 10 mg/10 mg/kg, the mean serum levels of MK-0787 and MK-0791 were 29.9 micrograms/ml and 18.1 micrograms/ml at 1 hour and 3.4 micrograms/ml and 1.3 micrograms/ml at 3 hours, respectively. The half-lives were 0.89 hour for MK-0787 and 0.99 hour for MK-0791. At the dose level of 20 mg/20 mg/kg, the mean serum levels of MK-0787 and MK-0791 were 46.3 micrograms/ml and 45.2 micrograms/ml at 1 hour and 5.5 micrograms/ml and 3.1 micrograms/ml at 3 hours, respectively. The half-lives were 0.97 hour for MK-0787 and 0.83 hour for MK-0791. At the dose level of 40 mg/40 mg/kg, the mean serum levels of MK-0787 and MK-0791 were 104.0 micrograms/ml and 80.9 micrograms/ml at 1 hour and 7.8 micrograms/ml and 5.9 micrograms/ml at 3 hours, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)