Relative potency of controlled-release oxycodone and controlled-release morphine in a postoperative pain model

Objective: The relative analgesic potency of single doses of oral controlled-release oxycodone and oral controlled-release morphine were compared in a randomized, double-blind trial using a postoperative pain model. Methods: Women (n = 169) with moderate to severe pain following abdominal hysterectomy received single oral doses of controlled-release oxycodone, 20 mg or 40 mg, or controlled-release morphine, 45 mg or 90 mg. Assessments were made at 30 min, 60 min, then hourly after dosing for 12 h or until remedication. Results: The most precise estimates of relative potency showed that controlled-release oxycodone was 1.8 times more potent than controlled-release morphine for total effect (95% confidence limits 1.09-2.42; lambda 0.44) and 2.2 times more potent for peak effect (95% confidence limits 0.96-4.59; lambda 0.71). Controlled-release oxycodone at doses of 20 mg or 40 mg was comparable with controlled-release morphine at doses of 45 mg or 90 mg, respectively, for total and peak analgesic effects. For the two higher doses, time to peak relief was approximately Ih shorter with controlled-release oxycodone than with controlled-release morphine. Most patients reported onset of analgesia within 1 h with all doses. Side effects were similar with the two opioids. Conclusion: Oral controlled-release oxycodone was twice as potent as oral controlled-release morphine in this single-dose, relative potency assay. When converting patients from oral morphine to oral oxycodone, an initial oral oxycodone dose of one-half the oral morphine dose is recommended.