Effect of cimetidine on the pharmacokinetics of temafloxacin

Cimetidine, a widely prescribed histamine H2-receptor antagonist, is known to interact with a variety of drugs; consequently, it is important to determine its potential for interaction with any new drug. The interaction between cimetidine and a new quinolone, temafloxacin, has been examined in an open randomised 2-period crossover study in 12 healthy adults. Half the volunteers received cimetidine 400mg 3 times daily for 8 days. On day 5, a single temafloxacin 400mg dose was administered. No other drugs were allowed during this period. The other volunteers did not receive cimetidine (or any other drugs) for an 8-day period except for temafloxacin 400mg on day 5. Blood and urine were sampled serially after temafloxacin administration and daily thereafter until the last day of the study. A 2-week washout period preceded crossover. Pharmacokinetic analyses showed that cimetidine did not affect the rate or extent of temafloxacin absorption, as evidenced by unchanged peak plasma concentration, time to peak plasma concentration, and terminal-phase volume of distribution. However, renal and total clearance values for temafloxacin were reduced by 19%, and elimination half-life and area under the concentration vs time curve were increased in the presence of cimetidine. The most likely mechanism underlying these effects is inhibition by cimetidine of tubular secretion of temafloxacin in the kidney. The lack of clinically significant adverse effects and the small magnitude of the reduction in temafloxacin clearance suggest that the interaction is of little clinical consequence.