Pharmacokinetics of diazepam administered rectally in geriatric patients: comparison of suppositories with rectal...

The pharmacokinetics of diazepam administered as suppositories or as a solution in rectal tubes were compared in six geriatric hospital patients. A single dose of 10 mg was administered in a cross-over study with a one week interval. There was no statistically significant difference in the bioavailability, the mean maximum serum concentration or the time of achievement of the maximum with these preparations. However, the peak serum concentration was somewhat higher with suppositories but the absorption was somewhat faster via rectal tubes. The serum N-desmethyldiazepam concentration increased during the whole 24 hour observation period, there was no difference between the preparations. Our results are in good agreement with most studies of the pharmacokinetics of diazepam. The basal substance of the suppository is of the utmost importance to the absorption of diazepam. The rectal tube for administration of diazepam did not have any advantage over the optimally formulated (a mixture of macrogols) suppository in geriatric patients. In fact, the use of rectal tubes is more expensive, the tube may not be completely emptied, and the solution may not be completely retained in the rectum.