Role of rectal route in treating cancer pain: a randomized crossover clinical trial of oral versus rectal morphine administration in opioid-naive cancer patients with pain

The aim of this double-blind, double-dummy, crossover study was to compare the efficacy, tolerability, and time of onset of analgesia after the administration of 10 mg of morphine hydrochloride via the oral and rectal routes in opioid-naive cancer patients with pain. Thirty-four patients with cancer pain and no previous opioid treatment were randomized to receive morphine hydrochloride 10 mg orally or rectally (in the form of a microenema) for 2 days. During days 3 and 4, a crossover took place. The scores of pain, nausea, and sedation (visual analog scale of 0 to 100) calculated as the percentage change from baseline (before opioid administration) were assessed at different intervals up to 240 minutes. The number of vomiting episodes was recorded. Parity tests and analysis of variance (ANOVA) were performed to compare the two administration routes. A significant difference in pain intensity was achieved 10 minutes after rectal administration compared with 60 minutes after oral administration. There was still a significant reduction in pain via the rectal route after 180 minutes versus via the oral route after 120 minutes. No significant difference was observed in the intensity of sedation, nausea, or number of vomiting episodes between the oral and rectal routes. A liquid solution of morphine is well absorbed via the rectal route. Rectal morphine is safe, effective, easy to manage, and inexpensive, with a rapid onset of action. Rectal morphine can be considered a valid alternative route for opioid administration and may also be used when rescue doses of morphine are required in patients regularly treated with oral or parenteral opioids.