[Bioavailability of codeine and paracetamol in a combination preparation following oral and rectal administration].

The plasma concentrations of acetaminophen (paracetamol) and codeine were determined in a cross-over study in twelve healthy volunteers after oral and rectal application of a compound preparation. The relative bioavailability from the two forms of application was also computed. The two active substances showed almost parallel plasma concentration paths, and thus were systemically available at the same time. The maximum levels in plasma were already reached after one to two hours. In both active substances the suppositories displayed a classical retardation effect. In contrast to acetaminophen the rectal absorption of codeine was almost as effective as the oral absorption. Thus this application form shows almost bioequivalency vis-à-vis the capsule form. Based on these results the rectal form of administration of codeine as well as the combination of this substance with acetaminophen can be regarded, from the pharmacokinetic point of view, as a rational enhancement of the treatment of various forms of pain.