Nifedipine enhances amoxicillin absorption kinetics and bioavailability in humans

Intestinal absorption of aminopenicillins in vitro uses the dipeptide carrier system. Recent experiments have reported calcium ion to be a cellular mediator of the regulation of electrolyte transport through the enterocyte membrane, especially the Na/H exchange which is partly responsible for the proton gradient energizing the carrier system. In order to assess the in vivo relevance of these data, we studied, in healthy volunteers, the influence of nifedipine, a calcium channel blocking agent, on the intestinal uptake of amoxicillin, a commonly prescribed and well-absorbed aminopenicillin. Results obtained show that 1) intestinal absorption kinetics of amoxicillin follows a zero-order process, which further substantiates the existence of a saturable carrier-mediated process for this antibiotic in humans and 2) calcium channel blockade significantly enhances both absorption rate (by 70%) and bioavailability of amoxicillin (by 21.4%) without modifying its distribution or elimination. These findings might suggest that nifedipine could enhance amoxicillin intestinal uptake by stimulating its active transport.