Does intravenous methadone provide longer lasting analgesia than intravenous morphine? A randomized, double-blind study.

A prospective, randomized, double-blind trial was designed to compare the duration of analgesia produced by intravenous morphine and methadone. Patients with intractable cancer-related pain were studied for 5-6 days. One-eighth of the patient's daily opiate requirement was supplied as an i.v. infusion of either morphine or methadone over a period of 15 min. when initiated by the patient using a patient-controlled analgesia device. Dosing intervals, pain intensity assessments and toxicity were evaluated. Twenty-three patients were randomized; 18 were fully evaluable. Ten of the evaluable patients received morphine, 8 received methadone. Dosing intervals did not change over the 5 days for either group. The mean dosing interval for the last 10 doses was 3.9 +/- 0.85 h for patients receiving morphine and 3.9 +/- 1.6 h for patients receiving methadone (P = NS). One patient receiving morphine and one taking methadone required only 2-3 doses/day for pain control. Pain intensity and relief were similar for both groups. All patients had adequate analgesia as determined by at least a 50% difference in pain intensity at peak relief. The duration of pain relief when repeated intravenous doses of these analgesics were given was similar throughout the entire study period although morphine and methadone have different serum half-lives (3 vs. 25 h). Parenteral methadone does not offer a clinically significant increase in the duration of analgesia in patients with severe pain secondary to cancer.