Measurement of the analgesic effects of aspirin with a new experimental algesimetric procedure.

Using controlled long lasting noxious squeeze stimuli applied to the interdigital webs we have tried to develop experimental methods allowing us to measure the effects of peripherally acting analgesics. In the present double-blind cross-over study with 12 subjects we tested the effects of aspirin (1000 and 1500 mg) vs. placebo on subjective pain induced by alternately applied 12 N (Newton) and 8 N stimuli. During the sessions blood samples were taken in regular intervals to measure acetylsalicylate (ASA)- and salicylate (SA)-plasma levels. Analyses of variance were computed with several psychophysical parameters. Both the '12 N' and the '8 N' ratings discriminated between placebo and aspirin, however, only the ratings obtained from the stronger stimuli discriminated between two doses of aspirin. Subsequently we computed analyses of covariance with the ASA- and SA-plasma levels as covariates. Significant (negative) correlations of pain ratings and SA-plasma levels were found for the high dose of aspirin, but there were no significant correlations of ASA levels and ratings.