[Characterization of the effect of analgesics on the assessment of experimental pain in man. Pethidine and tramadol in a double-blind comparison].

The effect of the opioid analgesics tramadol and pethidine on experimentally induced pain was investigated in a double blind study with healthy volunteers. Using a constant current shocker, compensating the changes of the skin resistance, a constantly increasing pain stimulus was produced. Detection-, pain-, and tolerance-thresholds were assessed before and three times after intravenous injection of either pethidine (1 mg/kg bodyweight), tramadol (2 mg/kg bodyweight) or placebo (NaCl). While the two analgesics caused an increase of all three thresholds the placebo did not cause any threshold changes. The rise of the detection threshold after application of tramadol and pethidine suggests a sedation effect. However, in relation to the analgesic effect this sedation effect is stronger with tramadol than with pethidine. With the dosage used in this experiment, there is no difference in the analgesic effect of tramadol and pethidine. Compensating for intra- and interindividual changes in skin resistance, the pain stimulation method used in this study provides a good quantification of the effects of analgesics.