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 controlle d-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 h ysterectomy received single oral doses of controlled-release oxycodone, 20 mg or 40 mg, or controlled-release morphine, 45 mg or 90 mg. Assessments we re made at 30 min, 60 min, then hourly after dosing for 12 h or until remed ication. Results: The most precise estimates of relative potency showed that control led-release oxycodone was 1.8 times more potent than controlled-release mor phine 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; lamb da 0.71). Controlled-release oxycodone at doses of 20 mg or 40 mg was compa rable with controlled-release morphine at doses of 45 mg or 90 mg, respecti vely, for total and peak analgesic effects. For the two higher doses, time to peak relief was approximately Ih shorter with controlled-release oxycodo ne than with controlled-release morphine. Most patients reported onset of a nalgesia 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 c ontrolled-release morphine in this single-dose, relative potency assay. Whe n converting patients from oral morphine to oral oxycodone, an initial oral oxycodone dose of one-half the oral morphine dose is recommended.