Concurrent administration of donepezil HCl and cimetidine: assessment of pharmacokinetic changes following single and multiple doses.

AIM The aim of this study was to examine the pharmacokinetics of donepezil HCl and cimetidine separately, and in combination, following administration of multiple oral doses. METHODS This was an open-label, randomized, three-period crossover study in healthy male volunteers (n=19). During each treatment period, subjects received single daily doses of either donepezil HCl (5 mg), cimetidine (800 mg), or a combination of both drugs for 7 consecutive days. Pharmacokinetic comparisons were made between groups for the day 1 and day 7 profiles. Each treatment period was followed by a 3-week, drug-free washout period. RESULTS On both day 1 and day 7, a statistically significant difference was observed between the donepezil and the donepezil + cimetidine groups in terms of the Cmax and AUC(0-24) values for donepezil. The combination group had an 11-13% greater Cmax and a 10% greater AUC(0-24) than the donepezil-only group. No significant difference was observed between the tmax of the two treatment groups on day 1, and no significant differences in tmax, t1/2 or the rate of drug accumulation (RA) were observed between the groups on day 7. Cimetidine pharmacokinetics were essentially unchanged by co-administration of the two drugs. The donepezil + cimetidine treatment group had a 20% greater maximum cimetidine concentration (Cmax) than the cimetidine-only group (P= 0.001) on day 1, but not on day 7, and no difference was observed in any of the other pharmacokinetic parameters examined. CONCLUSIONS Co-administration of donepezil HCl (5 mg) and cimetidine (800 mg) did not produce clinically significant changes in the pharmacokinetic profiles of either drug.