Colonoscopy in the investigation of drug absorption in healthy volunteers.

In order to evaluate the absorptive capacity of the colonic mucosa, colonoscopy was used to investigate in six healthy volunteers the colonic absorption of the nonsteroidal anti-inflammatory drug diclofenac (Voltaren). Oral and colonic administration of 100 mg of diclofenac resulted in comparable peak plasma concentrations and areas under the plasma concentration time curves. The apparent relative availability of diclofenac from the colon compared to the oral form, which was assumed to be 100%, ranged from 54% to 109% with a mean of 78%. There was no difference in absorption between application of the drug in the cecum and in the splenic flexure. This new indication for colonoscopy proved to be simple, well tolerated, and well suited for phase I studies with new drugs or formulations.