SY5555, a new oral penem, was pharmacokinetically and clinically evaluated in the pediatric field and the following results were obtained: 1. Pharmacokinetics Pharmacokinetics of SY5555 dry syrup (powder which is dissolved before use) was investigated in 64 children. At a dose level of 3 mg (potency)/kg, Cmax and T1/2 were 0.33 micrograms/ml and 0.95 hours (n = 1), respectively, in the non-fasting state. At a dose level of 5 mg/kg Cmax and T1/2 were 2.09 +/- 1.25 micrograms/ml and 1.20 +/- 1.07 hours, respectively, in the fasting state, and were 1.21 +/- 0.70 micrograms/ml and 1.33 +/- 0.90 hours, respectively, in the non-fasting state. At a dose level of 10 mg/kg, Cmax and T1/2 were 2.96 +/- 1.89 micrograms/ml and 0.89 +/- 0.43 hours, respectively, in the fasting state, and were 2.45 +/- 1.37 micrograms/ml and 1.17 +/- 0.53 hours, respectively, in the non-fasting state. At a dose level of 15 mg/kg, Cmax and T1/2 were 4.30 +/- 2.15 micrograms/ml and 0.82 +/- 0.09 hours, respectively, in the non-fasting state. Data of Cmax and AUC showed that plasma concentration of the drug depended on dose levels. Urinary recovery rates in the first 6 hours were 1.71% (n = 1) in the non-fasting state at a dose level of 3 mg/kg, 4.13 +/- 1.40% in the fasting state and 4.17 +/- 3.29% in the fasting and the non-fasting state, respectively at a dose level of 5 mg/kg, and 6.02% (n = 1) and 4.64 +/- 2.81%, respectively, at a dose level of 10 mg/kg. At a dose level of 15 mg/kg, urinary recovery rate in the first 6 hours was 7.97% (n = 2) in the non-fasting state. 2. Clinical results 1) Dry syrup The clinical efficacy of the SY5555 dry syrup was evaluated in 506 cases. SY5555 was administered at daily doses of 15-30 mg/kg divided into 3 equal doses to most patients. Daily doses of 12- < 18 mg/kg were given to 46.6% of the patients. The overall clinical efficacy rate was 92.9%, and this drug was effective in 93.0% of the 301 patients for whom the causative pathogens were identified, and in 92.7% of the 205 patients with infections for whom the causative pathogens were unknown. The efficacy rate at daily doses of 12 - < 18 mg/kg was 94.5% similar to those obtained at daily doses of 18- < 27 mg/kg (91.7%) or 27- < 33 mg/kg (91.3%). The bacteriological eradication rate was 82.3%.(ABSTRACT TRUNCATED AT 400 WORDS)