The pharmacokinetics of oxprenolol following oral and rectal dosing--a comparison of delivery systems and routes of administration.

Plasma oxprenolol concentrations were measured in eight healthy volunteers who received equivalent oral doses of the drug in the form of an aqueous solution and a 10/170 oxprenolol Oros drug delivery system. Absorption from the lower gastrointestinal tract was assessed by measurement of plasma concentrations after rectal administration of the pre-equilibrated Oros systems. Because three of the first four volunteers suffered local irritation, however, the other four volunteers received Slow Trasicor 160 mg orally as a comparative preparation. The rate of in vivo absorption after oral administration of the Oros system closely mirrored its in vitro release rate. Drug availability from Oros was reduced, however, and was equivalent to 77% of that from the oral solution. Oxprenolol was well absorbed from the rectum while the system was present in this segment of the gut. The reduced systemic availability in three of the volunteers could be accounted for largely by drug loss when the system was expelled. Slow Trasicor produced higher peaks but lower 24 h plasma concentrations than the orally administered Oros system. As judged from the relative areas under the plasma concentration-time curve, however, the availability of the drug from the two dosage forms was comparable.