Refill-Based Medication Use Quality Measures in Kidney Transplant Recipients: Examination of Proportion of Days Covered and Medication Possession Ratio

BACKGROUND: The Pharmacy Quality Alliance’s definition of proportion of days covered (PDC) and medication possession ratio (MPR) have not been examined as potential quality measures in the kidney transplant recipient population. OBJECTIVES: To (a) describe the frequency distribution of MPR and PDC using mycophenolic acid products in a real-world kidney transplant recipient population and (b) evaluate associations between MPR and PDC with late (> 90 days after transplantation) biopsy-proven acute rejection (BPAR). METHODS: This was a retrospective cohort study combining data from the Wisconsin Allograft Recipient Database with University of Wisconsin (UW) Health Specialty Pharmacy prescription claims and dispensing data from March 10, 2006, to June 30, 2012. Patients who met criteria for persistence filling mycophenolic acid prescriptions at UW Health Specialty Pharmacy in the first year following discharge from kidney transplantation surgery hospitalization were included. Patients were excluded if they were enrolled in a clinical trial, if they had BPAR within 90 days of transplantation, or if they did not have panel reactive antibody data available. PDC and MPR were calculated over 360 days after discharge, and multivariable analyses were performed to determine if there were associations between PDC or MPR with late BPAR within 3 years. RESULTS: This study included 388 patients. The incidence of 3-year late BPAR was 5.1% (n = 20). Characteristics of patients who experienced late BPAR were largely consistent with those who did not experience late BPAR, with the exception of number of hospital readmissions, which was higher among patients who experienced late BPAR. The frequency distribution of PDC and MPR exhibited a skewed left distribution, with a median PDC of 0.972 and a median MPR of 1.000. Higher PDC was associated with lower odds of late BPAR (OR = 0.041, 95% CI = 0.004-0.417) in multivariable analysis, as was a higher MPR (OR = 0.041, 95% CI = 0.004-0.419). CONCLUSIONS: MPR and PDC may be calculated from data available to pharmacies and health plans, and each was associated with 3-year late BPAR among patients who did not experience early BPAR. However, the construct validity of these medication adherence measures requires further study.