Emetic effects of morphine and piritramide

Background. Successful management of postoperative pain requires that adequate analgesia is achieved without excessive adverse effects. Opioid-induced nausea and vomiting is known to impair patients' satisfaction, but there are no studies providing sufficient power to test the hypothesis that the incidence of opioid-induced nausea and vomiting differs between mu-opioid receptor agonists. Thus, we tested the hypothesis that the incidence of vomiting and nausea differs between morphine and piritramide. Methods. In a prospective, randomized, double-blind fashion, we administered either morphine (n=250) or piritramide (n=250) by patient-controlled analgesia (PCA) for postoperative pain relief. We used a bolus dose of 1.5 mg with a lockout time of 10 min. Incidence and intensity (numerical rating scale) of postoperative nausea, vomiting, pain, patient satisfaction (score 0-10), side-effects (score 0-3) and drug consumption were measured. Results. Mean drug consumption did not differ between the piritramide and morphine groups (30.8 (SD 22.4) mg day(-1) vs 28.4 (21.8) mg day(-1)) during the first postoperative day and there were no significant differences in the overall incidence of nausea (30% vs 27%) and vomiting (19% vs 15%). Intensity of nausea correlated inversely (P=0.01) with morphine consumption but not with piritramide consumption. Pain scores both at rest (2.2 (1.9) vs 2.6 (2)) and during movement (4.4 (2.2) vs 4.9 (2.3)) were slightly but significantly less with morphine. Conclusions. Opioid-induced emesis was observed in about one-third of the patients using morphine and piritramide for PCA and the incidence of vomiting was one-half of that. Potential differences in the incidence of vomiting during PCA therapy between these mu-opioid receptor agonists can be excluded.