Eight healthy male subjects (Sub) were allocated randomly to one of two treatment sequences in a two period crossover design. The two treatment sequences were either Drug A given alone (A) in the first period followed by both Drug A and Drug C (AC) in the second period, or the reverse order was administered. A seven day washout period separated the two treatment periods. The pharmacokinetic variables area under the plasma concentration vs. time curve (AUC), maximum plasma concentration (Cmax), time of Cmax (Tmax), and the elimination rate constant (ERC), were calculated for each subject in each treatment period from plasma levels of each of the parent compound (P) Drug A, and its metabolite (M), based upon plasma samples taken at 0, 10, 20, 30, 40, 50 minutes; 1, 1.25, 1.5, 1.75, 2, 3, 4, 5, 6, 8, 10, 12, 16, 24, 30, and 36 hours post dose.

• For either the parent compound (P) Drug A , or its metabolite (M), does giving Drug C concurrently with Drug A affect either the extent (AUC, Cmax) or rate (Tmax) of absorption? What about the elimination rate constant (ERC)?
• Is the pharmacokinetic profile of Drug A in the presence of Drug C the same as for Drug A alone?
• For each pharmacokinetic variable separately, suppose you wanted to combine the information from the parent compound and the metabolite, how would you do this?
• For either the parent compound or the metabolite separately, how would you combine the information for AUC and Cmax?
• Is there an association, or a relationship, between the parent compound and the metabolite in any of the four endpoints?