• Franklin K Johnson, Jeffrey G Stark, Frederick A Bieberdorf, and Joe Stauffer.
• Alpharma Pharmaceuticals LLC, a wholly owned subsidiary of King Pharmaceuticals, Inc., Bridgewater, New Jersey, USA. franklinkjohnson@yahoo.com
• Clin Ther. 2010 Jun 1;32(6):1149-64.

BackgroundMorphine sulfate/sequestered naltrexone hydrochloride (HCl) (MS-sNT) extended-release fixed-dose combination capsules, approved by the US Food and Drug Administration (FDA) in August 2009 for chronic moderate to severe pain, contain extended-release morphine pellets with a sequestered core of the opioid antagonist naltrexone. MS-sNT was designed so that if the product is tampered with by crushing, the naltrexone becomes bioavailable to mitigate morphine-induced subjective effects, rendering the product less attractive for tampering.ObjectivesThe primary aim of this study was to compare the oral bioavailability of naltrexone and its metabolite 6-beta-naltrexol, derived from crushed pellets from MS-sNT capsules, to naltrexone solution. This study also assessed the relative bioavailability of morphine from crushed pellets from MS-sNT capsules and that from the whole, intact product.MethodsThis single-dose, randomized-sequence, open-label, 3-period, 3-treatment crossover trial was conducted in healthy volunteers. Adults admitted to the study center underwent a 10-hour overnight fast before study drug administration. Each subject received all 3 of the following treatments, 1 per session, separated by a 14-day washout: tampered pellets (crushed for >or=2 minutes with a mortar and pestle) from a 60-mg MS-sNT capsule (60 mg morphine/2.4 mg naltrexone); 60-mg whole, intact MS-sNT capsule; and oral naltrexone HCl (2.4 mg) solution. Plasma concentrations of naltrexone and 6-beta-naltrexol were measured 0 to 168 hours after administration. Morphine pharmaco-kinetics of crushed and whole pellets were determined 0 to 72 hours after administration. The analysis of relative bioavailability was based on conventional FDA criteria for assuming bioequivalence; that is, 90% CIs for ratios of geometric means (natural logarithm [In]-transformed C(max) and AUC) fell within the range of 80% to 125%. Subjects underwent physical examinations, clinical laboratory tests, and ECG at screening and study discharge and were monitored for adverse events (AEs) throughout the study.ResultsOf the 24 subjects enrolled in the study, 23 completed it. Most subjects were white (79%) and male (63%); the mean (SD) age was 39.3 (11.2) years and the mean weight was 77.6 (13.5) kg (range, 55.0102.5 kg). Plasma C(max) and AUC(0-t) of naltrexone after the administration of crushed pellets of MS-sNT (579 pg/mL and 1811 h . pg/mL, respectively) and naltrexone solution (584 pg/mL and 1954 h . pg/mL) were not significantly different; 90% CIs were 83.8% to 116% and 83.3% to 102%, meeting the regulatory requirements for assuming bioequivalence in this study population. Plasma naltrexone concentration was below the lower limit of quantitation (4.0 pg/mL) in 23 of 24 subjects (96%) after whole MS-sNT administration. Morphine AUC(0-t) was not significantly different whether MS-sNT was crushed (163 h . ng/mL) or administered whole (174 h . ng/mL), but C(max) was numerically higher (24.5 vs 7.7 ng/mL) and T(max) was numerically shorter (2.00 vs 7.03 hours) with MS-sNT crushed versus whole. The most commonly reported AEs were nausea (8/23 [35%], 10/24 [42%], and 3/23 [13%] subjects in the crushed, whole, and naltrexone groups, respectively) and emesis (6 [26%], 7 [29%], and 2 [9%]).ConclusionsIn this single-dose study, when pellets from MS-sNT were crushed, naltrexone appeared to be completely released and available to mitigate morphine-induced effects. When MS-sNT was administered whole, morphine was released in an extended-release fashion while naltrexone remained sequestered.

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