Oral tramadol, a μ-opioid agonist and monoamine reuptake-blocker, and morphine for strong cancer-related pain

Abstract

Opioid and spinal monoaminergic agonists have distinct analgesic properties, which may potentiate each other. Tramadol has both opioid and monoaminergic agonist actions. This initial study compared the analgesic and toxic effects of tramadol and morphine in patients with strong cancer pain. Pain control and side-effects with tramadol and morphine were compared in 20 cancer patients hospitalised for the treatment of strong pain. Doses of oral solutions of tramadol or morphine were individually titrated in the double-blind, randomized, cross-over study. Cross-over was after day 4, the day of statistical evaluation. The mean pain intensity (+/- SD) on a verbal rating scale (0 = none, 4 = unbearable) was similar with morphine (1.6 +/- 1.2, n = 17) and with tramadol (1.5 +/- 1.3, n = 16) on the fourth day of dosing. The mean daily doses on day 4 were 101 +/- 58 mg of morphine and 375 +/- 135 mg of tramadol, indicating a relative potency of 4:1 with oral dosing. The total number of side-effects per person was lower on the fourth day with tramadol (p < 0.05), as was the severity of nausea (p < 0.05) and constipation decreased with tramadol (p < 0.05). Three patients dropped out of the morphine group due to side-effects and 4 out of the tramadol group due to inadequate analgesia. Overall, 8 patients (40%) preferred morphine, 3 (15%) favoured tramadol and 9 (45%) expressed no distinct choice. Nurses rated pain control better with morphine (p < 0.03), but the tolerability of tramadol was judged superior (p < 0.002). In certain cancer patients with strong pain, tramadol achieved good pain control with fewer side-effects than morphine. The non-opioid mode of action may result in a different spectrum of analgesia and side-effects. Longterm studies are required to confirm this study of brief duration.