Analgesic and hemodynamic effects of a single 7.5-mg intravenous dose of morphine in patients with moderate-to-severe postoperative pain.

STUDY OBJECTIVES

To evaluate the analgesic and hemodynamic effects of a single dose of intravenous morphine 7.5 mg in patients experiencing moderate-to-severe postoperative pain, and to determine any gender differences in analgesic response.

DESIGN

Randomized, double-blind, parallel-group, multicenter study.

SETTING

Postanesthesia care unit of a university teaching hospital.

PATIENTS

Eighty-eight patients who underwent total abdominal hysterectomy or prostatectomy.

INTERVENTION

Thirty-seven patients received a single dose of morphine sulfate 7.5 mg and 51 patients received placebo, both administered intravenously for 1 minute.

MEASUREMENTS AND MAIN RESULTS

Overall, morphine had no significant effect on systolic or diastolic blood pressure, heart rate, oxygen saturation, or respiratory rate. Compared with baseline, morphine significantly reduced pain intensity at 2, 5, and 10 minutes after administration (p<0.05). The difference in pain intensity between patients who received morphine and those who received placebo, however, was significant only at the 5-minute time point (p<0.02). Patients receiving morphine also reported mild pain relief at 2 and 5 minutes after its administration. Peak analgesic effect was reported 2 minutes after its administration in three quarters of the patients. Significant gender differences also were observed in response to analgesic effect. In women, no significant differences in pain intensity were seen at any time between the morphine and placebo groups, whereas in men receiving morphine, pain intensity was significantly less at 2, 5, and 10 minutes compared with baseline and that seen in the placebo group. Women were generally more satisfied with their pain treatment than were men.

CONCLUSION

A single 7.5-mg intravenous bolus dose of morphine did not appear to provide adequate reduction in perceived pain intensity in patients with moderate-to-severe postoperative pain. In addition, in contrast to the findings of other experimental pain studies, our data suggest that women are more tolerant of postoperative pain than are men.