Offset Analgesia and The Impact of Treatment with Oxycodone and Venlafaxine: A Placebo-Controlled, Randomized Trial in Healthy Volunteers

Offset analgesia (OA) is a pain-modulating mechanism described as a disproportionately large decrease in pain intensity evoked by a discrete decrease in stimulus temperature. The role of the opioidergic, serotonergic and noradrenergic systems on OA remains unclear. The aim of this study was to evaluate whether OA is modulated by an opioid (oxycodone) and a serotonin and noradrenaline reuptake inhibitor (venlafaxine) in terms of psychophysical assessments. In this randomized, double-blinded, placebo-controlled cross-over study, 20 healthy male participants (mean age: 24.6 ± 2.5 years) received 10 mg oxycodone, 37.5 mg venlafaxine or placebo twice daily for 5 days in three periods. OA was induced by noxious thermal stimulation on the forearm at baseline and last day of treatment. A control session of constant stimulus intensity was included for comparison. OA magnitude was unaffected by oxycodone and venlafaxine (p = 0.20 and p = 0.90, respectively). Oxycodone affected the control paradigm where a decreased rating of pain intensity was observed compared to placebo (p = 0.001). OA could not be modulated by oxycodone or venlafaxine and may be a robust phenomenon in healthy volunteers and not suitable for exploring pharmacological mechanisms of analgesia in human beings.