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EUGENE R. VISCUSI, M.D., is Director, Acute Pain Management, Department of Anesthesiology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA. DAVID R. GAMBLING, M.B., B.S., FRCPC, is Staff Anesthesiologist, Sharp Mary Birch Hospital for Women, San Diego, CA, and Associate Clinical Professor, Department of Anesthesiology, University of California San Diego, San Diego. THOMAS L. HUGHES, PHARM.D., M.D., is Physician, Woodland Healthcare, Woodland, CA. GAREN Z. MANVELIAN, M.D., was Medical Director, Skye Pharmaceuticals Inc., San Diego.

Address correspondence to Dr. Viscusi at the Department of Anesthesiology, Jefferson Medical College, Thomas Jefferson University, 111 South 11th Street, Suite G-8490, Philadelphia, PA 19107 (eugene.viscusi{at}jefferson.edu).

Purpose. A pooled analysis of six clinical studies was conducted to describe the pharmacokinetics of extended-release epidural morphine sulfate. Methods. Data from six clinical studies evaluating extended-release epidural morphine sulfate in volunteers and abdominal or hip surgery patients were pooled and analyzed. Participants age 18 years or older received extended-release epidural morphine sulfate (2.5–40 mg) within 30 minutes of surgery initiation. Most participants received a test dose of 1.5% lidocaine with 1:200,000 epinephrine for epidural space identification 15 minutes before study drug administration. Blood samples were generally collected at 0.5, 2, 4, 8, 12, 18, 24, and 48 hours postinjection. Results. Standard epidural morphine sulfate exhibited a spike in drug release, producing higher peak concentrations (Cmax) than 5-mg extended-release epidural morphine sulfate, which produced more prolonged serum morphine concentrations. Using labeled doses of extended-release epidural morphine sulfate (10–20 mg), the Cmax was comparable to that for 5-mg standard epidural morphine sulfate, whereas the apparent terminal elimination half-life and area under the serum concentration–time curve were twofold to fourfold greater and consistent with dose-proportional exposure. The mean dose-normalized Cmax for extended-release epidural morphine sulfate was 25% higher for women versus men. Administering extended-release epidural morphine sulfate 15 minutes after the test dose mitigated any pharmacokinetic interaction. Extended-release epidural morphine sulfate demonstrated dose- related reductions in postoperative fentanyl consumption and pain intensity. Conclusion. A pooled analysis of six studies revealed that extended-release epidural morphine sulfate provided a more prolonged release of morphine compared with standard epidural morphine sulfate. Extended-release epidural morphine sulfate displayed a consistent pharmacokinetic profile among adults, with only slight variability between men and women in Cmax, which appeared to be mainly caused by differences in body weight. Index terms: Blood levels; Dosage; Drug administration routes; Excretion; Half-life; Morphine sulfate; Opiates; Pharmacokinetics; Release; Sex; Sustained action medications; Weight