• Helen Slater, Thomas Graven-Nielsen, Anthony Wright, and Stephan A Schug.
• School of Physiotherapy, Curtin Health Innovation Research Institute, Curtin University, Perth, Western Australia. h.slater@curtin.edu.au
• Pain Med. 2012 Sep 1;13(9):1235-46.

ObjectiveMusculoskeletal pain has been associated with N-methyl-d-aspartate (NMDA) receptor-mediated mechanisms. This randomized controlled trial (RCT) investigated the effect of the NMDA receptor antagonist ketamine (25 mg sublingually) on modulating experimental muscle pain.DesignTwo groups (N = 11/group) of age- and sex-matched healthy subjects performed eccentric exercise using the nondominant arm wrist extensors (time 0) to induce muscle soreness 24 hours later (time 1).InterventionImmediately prior to exercise, subjects were administered either a 25 mg ketamine lozenge or a placebo. At time 1, experimental muscle pain was augmented by injection of hypertonic saline into the extensor carpi radialis brevis (ECRB) muscle of the exercised arm.Outcome MeasuresPressure pain thresholds (PPTs), muscle soreness, muscle pain intensity (electronic visual analog scale [VAS]), and maximal wrist extension force were assessed at time 0 (pre- and postexercise) and at time 1 (pre-, during, and post saline-induced pain).ResultsRegardless of group, PPT was reduced at ECRB (P < 0.021) and at the common extensor origin (P < 0.034) at time 1 preinjection compared with time 0 pre-exercise. At time 1, elevated levels of muscle soreness and force attenuation were similar between groups compared with time 0 pre-exercise (P < 0.0001), and similar hypertonic saline-induced pain areas and pain intensity profiles were evident.ConclusionIn comparison with placebo, a single low-dose sublingual pharmacological intervention targeting the processes of sensitization via antagonism of NMDA receptors did not modulate the effects of acute experimentally induced mechanical hyperalgesia, suggesting a higher dose or repeat doses may be required.Wiley Periodicals, Inc.

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