Modification of cefixime bioavailability by nifedipine in humans: involvement of the dipeptide carrier system

We studied the action of nifedipine on the bioavailability of cefixime, a molecule absorbed via the gut wall dipeptide carrier system in the rat, and on the bioavailability of D-xylose, which is absorbed via a pH (and Na(+)-)-dependent transporter. Each compound was administered alone or in combination with 20 mg of nifedipine to eight healthy male volunteers. Nifedipine significantly increased the absorption rate of cefixime (20.7 +/- 4.3 versus 16 +/- 3.5 mg/h in the absence of nifedipine). The absolute bioavailability of cefixime alone was 31% +/- 6% compared with 53% +/- 1% (P < 0.01) in the presence of nifedipine. The observed peak concentrations in serum were significantly different (2.5 +/- 0.3 mg/liter without nifedipine and 3.7 +/- 1.1 mg/liter with nifedipine; P < 0.02). In contrast, nifedipine induced no significant differences in the pharmacokinetic profile of xylose following oral administration. We conclude that (i) cefixime is absorbed in humans by an apparently active process which can be enhanced by a calcium channel blocker, in this case, nifedipine; and (ii) nifedipine does not modify the activity of the pentose transporter.