In three open-label, randomized studies, healthy adults at a clinical research center received two single oral doses of original formulation and two single doses of Opana^® ER, each separated by a ≥7-day washout. Doses were administered under fasted conditions (study 1,
5 mg doses; study 2, 40 mg doses) or after a high-fat breakfast (study 3, 40 mg doses). Subjects administered 40 mg doses also received naltrexone. The primary endpoint was systemic oxymorphone exposure; the bioequivalence criterion was met if the 90% confidence intervals of the geometric mean ratio (Opana ER/ original formulation) for oxymorphone area under the curve from time 0 to the last measured concentration (AUC_0–t), AUC from time 0 to infinity
(AUC_0–inf), and maximum plasma concentration (C_max) were within 0.8–1.25.²

Oxymorphone plasma concentrations on Day 8 from a randomized, 3-period, 4-sequence, crossover study involving 24 healthy volunteers to evaluate the pharmacokinetics and dose proportionality of original formulation. Each subject received 3 of 4 possible dose strengths
(5 mg, 10 mg, 20 mg, and 40 mg) of original formulation. The three 8-day administration periods were separated by a 7-day washout. On Days 1 and 8, dose administration was to occur after an overnight fast. Subjects continued fasting until 4 hours after dose administration.³