Effect of Nifedipine on Morphine-Induced Analgesia

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Abstract
Experimental data show that opiates interfere with calcium influx in the cell and that some calcium-channel blockers are analgesic. We therefore studied the effect of the calcium-receptor blocker nifedipine on the analgesic effect of morphine in the rat, using tail-flick responses, and in humans, using measurements of the intensity of postoperative pain. In both the experimental animals and humans nifedipine significantly (P < 0.001) increased the analgesic effect of morphine independently of any effect on the metabolism of morphine. Respiratory and cardiovascular functions were not significantly changed by nifedipine. The data indicate that Ca2+ is important in mediating the analgesic effects of opiates and suggest that calcium-receptor blockers might find a place in the treatment of pain.