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A Comparative Study of 2 Sustained-Release Morphine Preparations for Pain in Advanced Cancer

Purpose: Several sustained-release morphine (SRM) formulations are available internationally. This study compared 2 such products available in the United States, SR1 and SR2. Patients and Methods: In an open-label study, patients with advanced cancer pain were randomized to receive SR1 or SR2 every 12 hours around-the-clock (ATC) for 5 days, with immediate release (IR) liquid morphine for rescue dosing (RD). Efficacy, safety, and patient acceptability were determined. Results: A total of 32 patients were evaluable for efficacy and toxicity. Pain scores, RD dosage, RD frequency over 5 days, RD within 3 hours before and after the scheduled SRM, and 8 of the 11 evaluated side effects were higher in the SR1 group. At presumed morphine steady state (day 3), pain scores (P = .05), RD dosage (P = .07), RD frequency (P = .07), and number of RD ±3 hours from scheduled SRM dose (P = .05) were consistently greater in the SR1 group (despite a higher median morphine dose in that group). There was a clinically important and directionally consistent trend that favored SR2, although not all were statistically significant. Patient preference favored SR2 (P < .05). Neither group had difficulty swallowing SR1 or SR2. Conclusions: This is the first study that directly compared two 12-hour SRM formulations. The data suggested, by multiple clinically important measures, that SR2 may provide superior analgesic efficacy and less toxicity compared to SR1. It also supports the concept that it cannot be assumed that different SR formulations of a given opioid are clinically equivalent. A larger study is needed to confirm our findings.