• E Martin, C Narjoz, X Decleves, L Labat, C Lambert, M-A Loriot, G Ducheix, C Dualé, B Pereira, and G Pickering.
• From University Clermont Auvergne, Department of Fundamental and Clinical Pharmacology of Pain, NeuroDol, F-63000 Clermont-Ferrand, France (E.M., C.D., G.P.) Inserm UMR-S1147, Saints-Pères University Centre, Paris, France (C.N., M.-A.L.) University Paris Descartes, Sorbonne Paris Cité, Paris, France (C.N., M.-A.L.) Assistance Publique-Paris Hospital (AP-HP), Georges Pompidou European Hospital, Biochemistry Department, Paris, France (C.N., M.-A.L.) Cochin Hospital, HUPC, Hôpitaux de Paris (AP-HP) Paris, France (X.D., L.L.) Pharmacy Faculty, University Paris Descartes Inserm UMR-S1144, Paris, France (X.D.) Clermont-Ferrand, Research and Innovation Department, Clermont-Ferrand, France (C.L., B.P.) University Hospital Clermont-Ferrand, Clinical Pharmacology Department/Clinical Research Centre, Inserm 1405, F-63003 Clermont-Ferrand, France (G.D., C.D., G.P).
• Anesthesiology. 2019 Aug 1; 131 (2): 356-368.

BackgroundCentral pain sensitization is often refractory to drug treatment. Dextromethorphan, an N-methyl-D-aspartate receptor antagonist, is antihyperalgesic in preclinical pain models. The hypothesis is that dextromethorphan is also antihyperalgesic in humans.MethodsThis randomized, double-blind, placebo-controlled, crossover study explores the antihyperalgesic effect of single and repeated 30-mg dose of oral dextromethorphan in 20 volunteers, using the freeze-injury pain model. This model leads to development of primary and secondary hyperalgesia, which develops away from the site of injury and is associated with central sensitization and activation of N-methyl-D-aspartate receptor in the spinal cord. The primary outcome was antihyperalgesia calculated with the area under the curve of the percentage change in mechanical pain threshold (electronic von Frey) on the area of secondary hyperalgesia. The secondary outcomes were mechanical pain threshold on the area of primary hyperalgesia and cognitive (reaction time) effect.ResultsSingle 30-mg results are reported. Antihyperalgesia (% · min) is significantly higher on the area of secondary hyperalgesia with dextromethorphan than placebo (median [interquartile range]: 3,029 [746; 6,195] vs. 710 [-3,248; 4,439], P = 0.009, Hedge's g = 0.8, 95% CI [0.1; 1.4]). On primary hyperalgesia area, mechanical pain threshold 2 h after drug intake is significantly higher with dextromethorphan (P = 0.011, Hedge's g = 0.63, 95% CI [0.01; 1.25]). No difference in antinociception is observed after thermal painful stimuli on healthy skin between groups. Reaction time (ms) is shorter with placebo than with dextromethorphan (median [interquartile range]: 21.6 [-37.4; 0.1] vs. -1.2 [-24.3; 15.4], P = 0.015, Hedge's g = 0.75, 95% CI [0.12; 1.39]). Nonserious adverse events occurrence (15%, 3 of 20 volunteers) was similar in both groups.ConclusionsThis study shows that low-dose (30-mg) dextromethorphan is antihyperalgesic in humans on the areas of primary and secondary hyperalgesia and reverses peripheral and central neuronal sensitization. Because dextromethorphan had no intrinsic antinociceptive effect in acute pain on healthy skin, N-methyl-D-aspartate receptor may need to be sensitized by pain for dextromethorphan to be effective.

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