Evaluating the Efficacy of Intranasal Oxytocin on Chronic Pain

Background and Importance: Chronic pain affects 1 in 5 Canadians and is associated with considerable burden, both individual (disability, reduced physical and emotional function) and economic ($43 billion annual cost to the economy). Available treatments for chronic pain rarely resolve symptoms, may be associated with addiction and often do not improve function. There is a need for analgesics that are non-addictive, have low adverse effect profiles, and offer effective relief. Our work suggests that oxytocin (OT), a neuropeptide produced in the hypothalamus, may be a safe and effective adjuvant analgesic for a broad patient population. There are three mechanisms through which OT may decrease pain sensitivity: 1) a direct hypothalamo-spinal projection transports OT to the dorsal horn, reducing pain signaling from the periphery to the brain; 2) binding to opioid receptors and stimulating endogenous opioid release in the brain; and 3) improving mood, anxiety, and stress. Our team published a systematic review of the effect of OT on pain showing that 29/33 animal investigations report that OT decreases pain. It is difficult to draw firm conclusions about the effect of OT on pain in humans due to a paucity of methodologically rigorous trials. Goals / Research Aim: To evaluate the efficacy of intranasal OT as an adjuvant treatment to improve pain and function among men and women with chronic pain. Methods: Design: Multi-site, dose-response, placebo-controlled, blinded, sequential, within-subjects crossover trial. Outcomes: As recommended by the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials, the primary outcome is change in pain-intensity assessed using the Brief Pain Inventory obtained from daily diaries. Conditions: Experimental 1: 2-week course of 24-IU intranasal OT administered twice daily. Experimental 2: 2-week course of 48-IU intranasal OT administered twice daily. Control: 2-week course of intranasal placebo. Wash-Out: 2-week period occurring between each condition to allow OT to clear the system. Recruitment: Patients with chronic neuropathic, musculoskeletal and pelvic pain will be recruited from 3 sites: Vancouver, Calgary, and St. John's. Patients will be randomized to one of 2 sequences (24-IU OT, placebo, 48-IU OT; placebo, 24-IU OT; 48-IU OT). Randomization will be centralized and stratified by site. Blinding: Patients, researchers, and outcome assessors will be blind to condition. Sample Size: 336 patients (112 per site) are required to detect a clinically significant (1-point; d = .50) change in pain using covariate adjusted repeated measures design with alpha = .05, power = .80, and one cluster (site). Expected Outcomes: Provide a definitive answer regarding the efficacy of OT to improve pain and function in chronic pain in humans. An efficacy trial of this nature is a necessary prerequisite to conducting a translation trial which is aimed at improving the uptake and utilization of proven therapies in clinical practice and community settings.