The aim of this study was to evaluate the effect of tapentadol and morphine on descending pain inhibition, represented by the conditioned pain modulation (CPM) test, in healthy volunteers. The results demonstrated that morphine negatively affects CPM, while tapentadol has no effect on CPM, confirming the different mechanism of action of the two drugs. Tapentadol and morphine are both opioid analgesics, tapentadol is a combined μ-opioid receptor (MOR) agonist and noradrenaline reuptake inhibitor; morphine is a strong mu-opioid receptor agonist without significant effect on noradrenaline reuptake. This study evaluated the influence of the above analgesic drugs on conditioned pain modulation (CPM) in healthy individuals and, based on the existing data, suggested that morphine will cause reduced CPM responses.
All 12 healthy volunteers attended 3 sessions, in each they were treated with a different drug (placebo, tapentadol and morphine). The CPM test was performed 60–90 and 120–150 min after drug intake.
The results demonstrated that morphine reduced CPM responses in comparison to placebo (by 80%). Tapentadol, in contrast to the hypothesis, had no effect on CPM responses compared to placebo treatment. The paper suggests various possible explanations of these findings. The data presented in the paper confirms the difference in main mechanism of action of the two drugs and suggests a possible explanation for these underlying mechanisms.
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