EFFECT OF ONDANSETRON, A 5-HT3 RECEPTOR ANTAGONIST, ON THE DYNAMIC ASSOCIATION BETWEEN BULIMIC BEHAVIORS AND PAIN THRESHOLDS

Thresholds for detection of both pressure and thermal pain are elevate d in patients with bulimia nervosa. The present study was aimed at det ermining (1) if pressure pain detection thresholds (PDT) varied dynami cally with the primary disease symptoms of binge eating and vomiting a nd (2) if the elevation in PDT was effected by treatment with ondanset ron (ONDAN), a 5-HT3 receptor antagonist. PDT was defined as the mean of the minimal amount of pressure (measured in g) perceived as painful when exerted by a 1 mm(2) blunted point onto the center of the ventra l surface of the ungual phalanx of digits 2-5 of the non-dominant hand . Fourteen female patients with severe bulimia nervosa (currently >sev en binge/vomit episodes per week, >2 years illness duration) served as participants. PDT were evaluated at weekly intervals during the cours e of ongoing treatment studies (double-blind and 'open' label) investi gating the therapeutic effects of ONDAN. Data were analyzed by random regression analyses, allowing for the repeated-measures and non-orthog onal design. Data collected from 14 patients under the no-drug conditi on indicated that PDT increased over the interval between binge/vomit episodes, with significant elevations occurring at times when patients had naturally exceeded their average inter-binge interval. Eleven of these 14 patients underwent 4 weeks of ONDAN treatment. Under this dru g condition, the time since the last binge/vomit episode was no longer a significant predictor of PDT. These patients also experienced a sig nificant reduction in the frequency of bulimic behaviors, a finding re ported in detail elsewhere. The above finding from untreated patients support the involvement of a common underlying mechanism driving both the increase in pain detection thresholds and the occurrence of the ne xt bulimic episode. This possibility is further supported by the findi ngs that ONDAN treatment is associated with a significant moderation o f both variables. The effect of ONDAN may be mediated by blockade of a fferent vagal neurotransmission, although other mechanisms must be con sidered. (C) 1998 International Association for the Study of Pain. Pub lished by Elsevier Science B.V.