Antiemetic effect of ondansetron 0.2 mg mL-1 in PCA morphine solution

To study the effect of 0.2 mg mL-1 of ondansetron added to morphine patient-controlled analgesia solution after a 4 mg loading dose on the incidence and severity of postoperative nausea and vomiting.

One hundred and sixty patients scheduled for elective surgery, between 18 and 65 yr old, were studied. Patients who smoked, received antiemetics and hormonal therapy, had a history of motion sickness or gastrointestinal disease, a body mass index >35 or menstruation at the time of the study were excluded. Patients were assigned to the ondansetron and control groups by block randomization. At the end of anaesthesia, all patients received 4 mg of ondansetron intravenously and the same patient-controlled analgesia regimen of morphine. The ondansetron group (n = 80) received 0.2 mg of ondansetron per 1 mg of morphine. The nausea score, vomiting score and the requested ondansetron dose were evaluated at 1, 2, 6, 12 and 24 h. Patient-satisfaction for nausea/vomiting was recorded at the end of the study.

Patient characteristics and cumulative morphine consumption were similar but ondansetron group had higher pain scores (P = 0.006). The ondansetron group had a lower nausea and vomiting scores, and more patients were free from nausea and vomiting than the control group (41 vs. 26, respectively, P = 0.025). The ondansetron group had fewer cumulative ondansetron doses than the control group and better patient satisfaction than the control group (P < 0.05).

Ondansetron 4 mg plus 0.2 mg mL-1 given with PCA morphine can reduce nausea and vomiting thus improving patient satisfaction.