A Comparison of Daily Average Consumption (DACON) of Oxycodone and Oxymorphone Long-Acting Oral Tablets

BACKGROUND: The utilization of high-potency opioids is an important component of chronic pain management, and appropriate utilization of these medicines is a common concern of payers. Two of the most commonly prescribed oral long-acting opioids, oxycodone controlled-release (CR) and oxymorphone extended-release (ER), are FDA-approved for twice-daily dosing, which equates to a theoretical average consumption (DACON) of 2 tablets per day. DACON values greater than 2 have budget and policy implications for managed care pharmacists. OBJECTIVES: To assess from the perspective of the pharmacy benefit decision maker the DACONs of oxycodone CR and oxymorphone ER. METHODS: The main outcome measure for the analysis was DACON. Pharmacy and medical claims data from a large commercially insured population (i3 InVision Data Mart database) were analyzed to identify patients with at least 1 pharmacy claim for either oxycodone CR or oxymorphone ER from July 1, 2007, to September 30, 2009. After an initial 30-day titration period, all subjects included in the study had 1 or more claims totaling at least a 90-day supply of either study drug during the subsequent 90 days (DACON measurement period). Patients were excluded if there was evidence of a switch from one to the other study opioid during the 90-day measurement period. There were no limitations on the use of other opioids, either short- or long-acting, during either the DACON measurement period or the previous 6 months (baseline period). In addition, patients were excluded if the enrollee was younger than 18 years old, pregnant, did not have continuous insurance coverage for the 6 months before and after the start of the 90-day DACON measurement, or were enrolled in an HMO plan. Bivariate analyses were performed with between-group differences in DACON values assessed using t-tests and Wilcoxon rank sum tests. Patient characteristics including age, sex, geographic location, and baseline Charlson Comorbidity Index (CCI) for each drug group were evaluated descriptively using either the Pearson chi-square test or t-test. Multivariate analyses were conducted using generalized linear models (GLM) to adjust for the observed heterogeneity among patients in the observational database. For the GLMs, the gamma distribution and log link function were chosen to account for non-normal distributions of DACON. Independent variables included study drug, tablet strengths, age, sex, CCI, the maximum days gap between prescription refills during the DACON measurement period, and other opioid medication use. Several sensitivity analyses were conducted to verify all findings. RESULTS: The final analyses were conducted on 6,567 oxycodone CR patients and 796 oxymorphone ER patients. The unadjusted DACON mean value for the highest strength of oxycodone CR 80 milligrams (mg) was 3.9, compared with 2.9 for oxymorphone ER 40 mg (P less than 0.001); mean DACON values were 3.0 versus 2.4, respectively, for lower strengths (P less than 0.001) and 3.1 versus 2.5 for all strengths (P less than 0.001). After adjusting for age, sex, CCI, maximum gap days, and other opioid medication use, a risk-adjusted mean difference in DACON remained, with oxycodone CR patients receiving on average 0.6 tablets more per day than those dispensed oxymorphone ER (P less than 0.001). The direction, magnitude, and statistical significance of these differences were essentially unchanged in sensitivity analyses. CONCLUSIONS: On average during a 90-day time period, patients taking oxymorphone ER consumed 0.6 fewer tablets per day than did patients taking oxycodone CR. Further research is necessary to see if this difference amounts to cost savings for health plans that provide prescription reimbursement for patients with chronic pain syndromes.