Reduced ampicillin bioavailability following oral coadministration with chloroquine.

Ampicillin bioavailability was examined in seven healthy adult male volunteers after oral coadministration with chloroquine using the urinary excretion method. Ampicillin (500 mg, capsules) and chloroquine phosphate (250 mg, tablets) were administered in single doses of 1.0 g each. Each subject received, on two different occasions, ampicillin alone and ampicillin together chloroquine. Urine was collected hourly for 8.0 h. Ampicillin urinary levels were measured chemically. The mean % dose excreted, maximum peak of excretion and the time of that peak after the administration of ampicillin alone were: 29 +/- 4.1%, 1.73 +/- 0.27 mg/min and 1.75 +/- 0.164 h, respectively. The corresponding values after coadministration of ampicillin with chloroquine were: 19 +/- 2.9%, 1.25 +/- 0.17 mg/min and 1.82 +/- 0.210 h. The results indicate a significant reduction (P less than 0.005) in ampicillin bioavailability following oral coadministration with chloroquine. The reduction of ampicillin bioavailability produced by chloroquine might be attributed to slowing of gastric emptying and enhancement of gut motility induced by the chloroquine.