[Postoperative pain therapy. The efficacy of a serotonin antagonist (GR 38032F;ondansetron) and the prostaglandin synthesis inhibitor lysin acetylsalicylate (Aspisol)].

Serotonin is one of the many neurotransmitters involved in nociception. Serotonin antagonists may therefore reduce postoperative pain. In the present study we examined whether the new 5-HT3 receptor antagonist GR 38032F (ondansetron) reduced postoperative pain after minor surgery and compared its effectiveness with that of lysin acetyl salicylate (Aspisol). METHODS. A series of 100 patients of both sexes who were undergoing minor surgery were enrolled in this study. Patients who did not need analgesic medication within the first 3 h after surgery were regarded as "dropouts", and the rest were studied for 24 h. In a preliminary study (n = 19) patients received ondansetron i.v. in increasing dosages (6, 12, 24, 48, 96 and 128 micrograms.kg-1) to evaluate the analgesic potency of this drug. In the main double-blind, randomized, study (n = 81), three groups were formed, and patients received 50 micrograms.kg-1 or 100 micrograms.kg-1 ondansetron i.v. or saline only i.v. Analgesia was evaluated by visual analogue (VAS) and verbal rating scales (VRS). If pain persisted patients received 1.8 g lysin acetylsalicylate (LAS) i.v. RESULTS. There were 6 (out of 19) patients in the preliminary study and 36 (out of 81) patients in the main study who were dropouts; that is to say they did not require any analgesic medication within the first 3 h, but 12 of these dropouts needed analgesic medication more than 3 h after end of surgery. Pain was reduced by 82% from baseline in 7 out of 13 patients in the preliminary study (11 men, 2 women). In the main study (n = 45, 28 men, 17 women) 100 micrograms.kg-1 ondansetron did not show a better analgesic effect than 50 micrograms.kg-1, and there was no significant difference between ondansetron and saline. VAS showed a reduction in pain from 6.9 +/- 2.0, 6.8 +/- 1.5 and 6.6 +/- 1.8 to 4.1 +/- 2.4, 3.4 +/- 2.2 and 3.4 +/- 2.1 in the 50 micrograms.kg-1, 100 micrograms.kg-1 and saline groups, respectively, within 60 min after i.v. application. VRS diminished from 2.5 +/- 0.5, 2.5 +/- 0.6 and 2.4 +/- 0.5 to 1.7 +/- 0.7, 1.5 +/- 0.8 and 1.5 +/- 0.7, respectively. There were 26 patients who experienced no pain relief in response to ondansetron or placebo and who therefore received LAS, and 21 of these then experienced significant pain reduction. CONCLUSION. Pain after minor surgery does not appear to be a major problem. For 42 out of 100 patients no analgesics were needed within the first 3 h after end of surgery. Ondansetron was no more effective than placebo in reducing postoperative pain. Lysin acetylsalicylate, however, may be an effective alternative to opioids for the treatment of postoperative pain.