Cefditoren pivoxil (CDTR-PI, ME1207) granules, a new oral cephem, was given to pediatric patients with infectious diseases to evaluate antibacterial activities against clinical isolates, pharmacokinetics, clinical efficacy and safety, and the following results were obtained. 1. In sensitivity test, 30 strains were used comprised of 5 species, isolated from the patients before administered with CDTR-PI. Against Staphylococcus aureus, MICs of 7 agents, cefditoren (CDTR), cefaclor, cefixime, cefteram, cefotiam, cefpodoxime and methicillin, were determined. Against other 4 species, MICs of the above 6 agents excluding methicillin were determined. Among Gram-positive cocci tested, the MICs of CDTR were 0.78 to 100 micrograms/ml or higher against S. aureus (16 strains), < or = 0.025 microgram/ml against Streptococcus pyogenes (5 strains), and 0.10 or 0.39 microgram/ml against Streptococcus pneumoniae (2 strains). These values were equal to or lower than those of conventional cephems and of methicillin. Among Gram-negative rods tested, the MICs of CDTR were < or = 0.025 microgram/ml against Haemophilus influenzae (3 strains), and 0.10 or 0.20 microgram/ml against Escherichia coli (4 strains). Also, these values were equal to or lower than those of conventional cephems. 2. When CDTR-PI granules was orally administered in a single dose of 3.0 mg/kg to 1 patient and that of 6.0 mg/kg to 2 patients 30 minutes after meal, plasma CDTR concentrations reached their maxima 4 hours after administration in the former patient and 1 or 2 hours after administration in the latter 2 patients, and the peak plasma concentrations were 1.91, 3.46 and 4.82 micrograms/ml with half-lives of 1.01, 0.81 and 0.88 hours and AUCs of 8.62, 9.89 and 13.52 micrograms.hr/ml, respectively. Dose-dependency was observed for the peak plasma concentrations and AUCs also tended to depend on dose excepting for the AUC in one 6.0 mg/kg patient. 3. The urinary concentrations in the above patients reached their peaks at 4 to 6 hours after administration in one 3.0 mg/kg patient and at 4 to 6 hours and 2 to 4 hours after administration in two 6.0 mg/kg patients, and the corresponding values were 126.0, 195.0 and 234.0 micrograms/ml, respectively. Recovery rates in the first 8 hours after administration were 18.2, 24.6 and 21.3%, respectively. 4. Of 53 patients with 13 diseases, CDTR-PI was clinically judged "excellent" in 32 (60.4%) and "good" in 21 (39.6%), showing excellent efficacy. 5. Bacteriologically, excellent results were obtained, i.e., 29 (96.7%) of 30 strains from 5 species were eradicated. 6. Side effects were observed in none of the 54 patients treated.(ABSTRACT TRUNCATED AT 400 WORDS)