Relative variability in bioavailability of oral controlled-release formulations of oxycodone and morphine

A retrospective analysis compared the coefficients of variation associated with the maximum plasma concentration (Cmax) and the extent of absorption (area under the curve [AUC] from 0 hour to the last observation) for oral, controlled-release tablet formulations of oxycodone (OxyContin) and morphine (MS Contin). Data from fasting, male subjects aged 18 to 45 years were taken from five controlled-release oxycodone (N = 82) and seven controlled-release morphine (N = 101) single-dose, bioequivalence studies. The coefficients of variation of Cmax and AUC were approximately 33% less for controlled-release oxycodone than for controlled-release morphine (P =.005). The variation from the minimum to maximum value was two to three times less for controlled-release oxycodone than for controlled-release morphine. Among healthy male subjects, the absorption of oxycodone from oral controlled-release oxycodone was significantly more consistent than the absorption of morphine from oral controlled-release morphine in terms of both maximum absorption and extent of absorption.