Analgesic and antihyperalgesic effects of melatonin in a human inflammatory pain model: a randomized, double-blind,...

Antinociceptive effects of melatonin have been documented in a wide range of experimental animal models. The aim of this study was to investigate the analgesic, antihyperalgesic, and anti-inflammatory properties of melatonin using a validated burn injury (BI) model in healthy male volunteers. The design was a randomized, double-blind, placebo-controlled, three-arm crossover study. Each volunteer participated in 3 identical study sessions with intravenous administration of placebo, melatonin 10 mg, or melatonin 100 mg. Sixty minutes after bolus injection of study medication, a BI was induced by a computerized contact thermode (47.0°C, 420 seconds, 5.0 × 2.5 cm). Pain ratings during the BI and quantitative sensory testing at baseline and at 1, 2, 4, and 6 hours after the BI were performed. Quantitative sensory testing included assessments of secondary hyperalgesia areas, mechanical and thermal thresholds in the BI area, and pressure algometry. Furthermore, markers of inflammation, skin-reflectance spectrophotometry, and high-resolution ultrasonography were applied to measure skin erythema and dermal thickness in the BI area. Pain during the BI and secondary hyperalgesia areas were defined as primary outcomes. Twenty-nine volunteers were randomized and completed the study. While the BI induced large secondary hyperalgesia areas and significantly increased the markers of inflammation, no significant effects of melatonin were observed with respect to primary or secondary outcomes, compared with placebo. The administration of melatonin was not associated with any adverse effects. Melatonin did not demonstrate any analgesic, antihyperalgesic, or anti-inflammatory properties in the BI model.