<i>Harpagophytum procumbens</i> extract potentiates morphine antinociception in neuropathic rats

<p>The association of opioids and non-steroidal anti-inflammatory drugs, to enhance pain relief and reduce the development of side effects, has been demonstrated. Given many reports concerning the antinociceptive and anti-inflammatory effects of <i>Harpagophytum procumbens</i> extracts, the aim of our study was to investigate the advantage of a co-administration of a subanalgesic dose of morphine preceded by a low dose of <i>H. procumbens</i> to verify this therapeutically useful association in a neuropathic pain model. Time course, registered with the association of the natural extract, at a dose that does not induce an antinociceptive effect, followed by a subanalgesic dose of morphine showed a well-defined antiallodynic and antihyperalgesic effect, suggesting a synergism as a result of the two-drug association. <i>H. procumbens</i> cooperates synergistically with morphine in resolving hyperalgesia and allodynia, two typical symptoms of neuropathic pain. The results support the strategy of using an adjuvant drug to improve opioid analgesic efficacy.</p>