The bioavailability of morphine in controlled-release 30-mg tablets per rectum compared with immediate-release 30-mg...

The bioavailability of controlled-release morphine 30-mg tablets (MSC) administered orally or rectally and immediate-release morphine (RMS) 30-mg suppositories per rectum, was compared in this 14-subject, randomized, single-dose, analytically blinded, crossover study. Rectal MSC plasma morphine area under the curve from 0-24 hours (AUC0-24) was 50.8% of RMS and was similar for MSC administered by either route (rectal MSC = 90% oral MSC). Rectal MSC had a significantly delayed time to peak plasma level (5.4 vs 1.07 and 2.5 hrs for rectal MSC vs RMS and oral MSC, respectively) and a significantly attenuated time to maximum concentration (6.1 vs 25.4 and 9.7 ng/ml, respectively). Proctoscopy 24 hours after insertion revealed seven instances of mild, transient mucosal erythema or edema with rectal MSC and 12 with RMS. The number of nonlocal adverse effects was 14 with rectal MSC, 19 with RMS, and 18 with oral MSC. Further studies must determine the therapeutic consequences of pharmacokinetic differences and establish guidelines for rectal MSC use. The product is currently not recommended by the manufacturer for rectal administration.