Preliminary results from a randomized, controlled, cross-over trial of intrathecal oxytocin for neuropathic pain.

Objective: Compare intrathecal oxytocin, 100 µg to placebo on ongoing neuropathic pain and mechanical hyperalgesia and allodynia.

Study Design: Randomized, controlled, double-blind cross-over.

Setting: Clinical research unit.

Subjects: Individuals aged 18 to 70 years with neuropathic pain for at least 6 months.

Methods: Individuals received intrathecal injections of oxytocin and saline, separated by at least 7 days, and ongoing pain in neuropathic area (VAS [visual analog scale]) and areas of hypersensitivity to von Frey filament and cotton wisp brushing were measured for 4 hours. Primary outcome was VAS pain in the first 4 hours after injection, analyzed by linear mixed effects model. Secondary outcomes were verbal pain intensity scores at daily intervals for 7 days and areas of hypersensitivity and elicited pain for 4 hours 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 = .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 = .001). Allodynic area decreased by 11%, but hyperalgesic area increased by 18% after oxytocin compared to placebo. There were no study drug related adverse effects.

Conclusion: 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.

Trial Registration: This study was registered at ClinicalTrials.gov on 03/27/2014 (NCT02100956). The first subject was studied on 06/25/2014.