OBJECTIVES: Although both oxycodone CR and oxymorphone ER are approved for twice daily dosing, it is unclear whether actual utilization is consistent with this.  The objective was to assess whether there exist differences in the utilization of oxycodone CR and oxymorphone ER. METHODS: We used prescription claims data from a commercially-insured population (i3 InVision Data Mart database), during the period January 1, 2007 to March 31, 2010.  A claim for at least one 30-day supply of study drug one month prior to the observation period was necessary to avoid capturing utilization associated with titration. Subsequently, all subjects had a claim for at least a 90-day supply of the respective opioid analgesic.  Patients’ claims were excluded from this analysis if there was evidence of a switch from one to the other study opioid during the 90-day observation period. There were no limitations on the use of other opioids, during the baseline or observation periods.  The final cohort consisted of 6,567 oxycodone CR patients and 796 oxymorphone ER patients.  In addition to univariate analysis, multivariate analyses were conducted using generalized linear models (GLM) to adjust for the observed heterogeneity among patients in the observational database. RESULTS: The unadjusted daily average supply (DASUP) mean values for the highest strengths of oxycodone CR (80 mg) was 3.9 compared to 2.9 for oxymorphone ER (40mg), 3.0 vs. 2.4 for all lower strengths, and 3.1 vs. 2.5 for all strengths. (all  p<0.001). After adjusting for baseline differences, a risk-adjusted overall mean difference in DASUP remained with oxycodone CR patients receiving, on average, 0.6 tablets more per day than those dispensed oxymorphone ER (p<0.001). The direction, magnitude and statistical significance of these differences were essentially unchanged in sensitivity analyses.    CONCLUSIONS: In managing the pharmacy benefit, decision-makers may want to consider the financial implications of these DASUP differences.