THE HYPOALGESIC EFFECT OF IMIPRAMINE IN DIFFERENT HUMAN EXPERIMENTAL PAIN MODELS

In a randomized, placebo-controlled, double-blind, cross-over study, t he hypoalgesic effect of a single oral dose of 100 mg imipramine was i nvestigated in 12 healthy volunteers. Test procedures performed before , 3, 6, and 9 h after medication included determination of (1) pain de tection and tolerance thresholds to heat and pressure; (2) the thresho lds of quadriceps femoris muscle withdrawal reflex to single and repea ted electric stimulation of the sural nerve; (3) amplitude of the refl ex evoked by 1.5 times the premedication reflex threshold; and (4) con tinuous pain rating during the cold presser test. Imipramine significa ntly increased pain tolerance thresholds to heat (P = 0.03) and pressu re (P = 0.01), and both the psychophysical pain tolerance threshold an d the reflex threshold to single electric stimulation (P = 0.02 and P = 0.03, respectively). On the repeated stimuli, which consisted of 4 p ulses given at 3 Hz, imipramine induced a significant increase in the threshold at which the pain summated through the stimulation series (P = 0.03), whereas the increase in the threshold at which the reflex su mmated was not significant (P = 0.09). Pain detection thresholds to he at and pressure, the amplitude of the reflex to single suprathreshold stimulation, and pain ratings during the cold presser test were unalte red by imipramine. It is concluded that imipramine has a differential hypoalgesic effect on different human experimental pain tests. This pr ovides new possibilities of assessing the differential effect of diffe rent tricyclic antidepressants on different pain modalities and intens ities.