SY5555, a new oral penem, in the form of dry syrup (powder which is dissolved before use) was evaluated for its pharmacokinetics and clinical efficacy in pediatric patients. Oral administration of 5 mg/kg and 10 mg/kg of SY5555 in dry syrup resulted in respective maximum plasma concentrations of 1.08 +/- 0.38 micrograms/ml (n = 4) and 2.50 +/- 1.81 micrograms/ml (n = 4), half-lives (T 1/2) of 2.72 +/- 1.86 hours (n = 3) and 1.14 +/- 0.88 hours (n = 4), and urinary excretion until 6 hours of 4.7% (n = 1) and 3.86 +/- 2.01% (n = 4). Clinical efficacy was evaluable in 22 patients, and the overall efficacy rate was 100%. As for bacteriological efficacy, all 5 strains of pathogenic organisms identified were eradicated (eradication rate, 100%). No remarkable adverse reactions or abnormal laboratory values were observed.