Experimental pain induced by electrical and thermal stimulation of the skin in healthy man: sensitivity to 75 and 150 mg diclofenac sodium in comparison with 60 mg codeine and placebo.

Models with experimentally induced pain in healthy man might be useful for the screening for analgesic effects of new drugs. Experimental pain models have been shown to discriminate reliably between the effects of opioid analgesics and placebo but their sensitivity to nonsteroidal anti-inflammatory agents is disputed. This study investigated whether it would be possible by using electrically and thermally induced cutaneous pain to discriminate reliably the effects of single oral doses of 75 and 150 mg diclofenac sodium on the one hand and 60 mg codeine on the other from those of placebo. Forty-eight healthy subjects participated each in four experiments in which they received, in random double-blind fashion, each of the treatments. Every experiment comprised eight series of measurements, two before and six after drug administration, carried out at 30 min intervals. Diclofenac sodium produced significant dose-related increases of threshold and tolerance to electrically and threshold to thermally induced pain. Codeine 60 mg was significantly superior to placebo in all pain measures. Its analgesic effects were stronger than those of diclofenac 75 mg but weaker than those of diclofenac 150 mg. Neither 150 mg nor 75 mg diclofenac caused more side effects than placebo, whereas codeine 60 mg elicited a high frequency of side effects. No severe adverse effects occurred after any one treatment. The results suggest that both electrically and thermally induced cutaneous pain are well suited to evaluate analgesic effects not only of opioids but also of nonsteroidal anti-inflammatory drugs.