Intrathecal oxytocin for neuropathic pain: A randomized, controlled, cross-over trial

Objective: To investigate the effect of intrathecal oxytocin compared to placebo on pain and hypersensitivity in individuals with chronic neuropathic pain. Study design: Randomized, controlled, double-blind cross-over study Setting: Outpatient clinical research unit. Subjects: Individuals between ages of 18 and 70 years with neuropathic pain caudal to the umbilicus for at least 6 months. Methods: Individuals received two blinded intrathecal injections of either oxytocin or saline, separated by at least 7 days, and ongoing neuropathic pain (VAS: visual analog scale) and areas of hypersensitivity were measured at intervals for 4 hours. The primary outcome was VAS pain, analyzed by linear mixed effects model. Secondary outcomes were verbal pain intensity scores at intervals for 7 days and areas of hypersensitivity and elicited pain for 4 hr after injections. Results: The study was stopped early after completion of 5 of 40 subjects planned due to slow recruitment and funding limitations. Pain intensity prior to injection was 4.75 +/- 0.99 and modeled pain intensity decreased more after oxytocin than placebo to 1.61 +/- 0.87.and 2.49 +/- 0.87, respectively (p=0.003). Daily pain scores were lower in the week following injection of oxytocin than saline (2.53 +/- 0.89 vs 3.66 +/- 0.89; p=0.001). Hypersensitivity differed between oxytocin and placebo by small amounts in opposite directions depending on modality tested. There were no study drug related adverse effects. Discussion: Although limited by the small number of subjects studied, oxytocin reduced pain more than placebo in all subjects. Further study of spinal oxytocin in this population is warranted.