Oxprenolol absorption in man after single bolus dosing into two segments of the colon compared with that after oral dosing

The systemic availability of oxprenolol after colonic and oral administration has been compared in a crossover study involving six healthy male volunteers. Drug administration into two regions of the colon (caecum and left flexure) was achieved by means of a colonoscopic technique. There were no obvious differences in plasma concentrations after drug administration to the caecum and left flexure, although in one subject it was necessary to repeat colonic administration because of unexpectedly high plasma drug levels on the first occasion. The possible reasons for this abnormal response are discussed. The mean systemic availability of oxprenolol was 82% after colonic compared with oral dosing, although marked differences were observed in individual plasma levels following drug administration by the two routes. The results of this study support the concept of extending the duration of oxprenolol release from a rate‐controlled dosage form to permit once‐ daily administration with this short elimination half‐life drug.