Effect of ampicillin on mefloquine pharmacokinetics in Thai males.

The kinetics of a single oral dose of mefloquine given either alone or with ampicillin has been studied in 8 healthy Thai male volunteers. There was a significantly higher maximum whole blood mefloquine concentration after coadministration with ampicillin (1648 vs 1228 ng.ml-1), as well as a significantly reduced terminal half life (15.3 vs 17.7 days), mean residence time (20.1 vs 23.4 days) and volume of distribution at steady state (14.1 vs 19.4 l.kg-1). Although there was no significant change in the AUC from zero time to infinity, the AUC from zero time to 5 days was significantly increased by ampicillin (4.86 vs 3.27 micrograms.ml-1 day). These changes in mefloquine disposition after antibiotic treatment may be due both to an increase in fractional bioavailability and a reduction in the enterohepatic recycling of mefloquine.