Effects of antacids on pharmacokinetics of cefditoren pivoxil and its metabolism in humans.

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The pharmacokinetics of a newly established oral cephem, cefditoren pivoxil (CDTR-PI), were studied in healthy adult volunteers. 1. The effects of antacids (aluminium hydroxide gel and cimetidine) on the pharmacokinetics ofCDTR-PI were investigated. There were no significant differences in serum levels or urinaryexcretion ratios of cefditoren, the active form of CDTR-PI, and cefditoren Δ3 between the groupsgiven CDTR-PI in combination with aluminium hydroxide gel or CDTR-PI alone. In contrast, themaximum serum concentration of cefditoren was significantly lower in the coadministration groupreceiving CDTR-PI and cimetidine than in the group given CDTR-PI alone. But no significantincrease was found in serum levels of cefditoren Δ3 or its urinary excretion rates between the twogroups. 2. Metabolism of CDTR-PI was studied in the group given the drug (200mg) alone. CDTR-PI was not detected in either serum or urine. Cefditoren existed mainly in serum and the isomer of cefditoren, cefditoren Δ3 was also detected. The urinary excretion rate of cefditoren was 22.9% 24 hours after oral administration of CDTR-PI. In addition, cefditoren, cefditorenΔ3, cefditoren E and MOH were detected in the urine. Pivalic acid, a metabolite derived from the ester moiety of CDTR-PI, was detected in serum and urine. Pivalic acid was excreted as a conjugate into urine and its excretion rate was 92% of the original dose.