Impact of Medicare part D on adherence and persistence to statin medications for Texas dual-eligible beneficiaries
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Statins are commonly used for treating the elevation of lipids in the blood stream, also known as hyperlipidemia. Statins are considered to be an economical and effective way to achieve desirable long-term health outcomes for hyperlipdemic patients, however, ensuring adequate adherence to statin medications is often difficult as hyperlipidemia is an asymptomatic condition and patients sometimes fail to recognize the importance of being adherent to their statin medications. The purpose of this study was to evaluate impact of enrollment under Medicaid and Medicare Part D and patient out-of-pocket costs on patient statin adherence, persistence, and mean number of gap days per claim. A retrospective claims database was used in this study to conduct repeated measures analyses on statin prescription claims from independent community pharmacies in Texas. The pre-period in this study extended from January 1, 2005 to September 30, 2005 (Medicaid period) and the post-period extended from January 1, 2006 to September 30, 2006 (Medicare period). The study population consisted of dual-eligible beneficiaries in Texas who had at least two stain claims in the pre and post-periods each. The final study population comprised of 1734 Texas dual-eligible beneficiaries with 6064 statin claims during the pre-period and 7956 claims during the post-period. Patients had an average of 3.49 statin claims during the pre-period and 4.58 statin claims during the post-period. Patients were dispensed an average of 57.34 days of drug supply per claim during the pre-period and 42.02 days of drug supply per claim during the post-period. The results from this study showed that out-of-pocket costs for patients increased from $0.39 per claim under Medicaid to $13.36 per claim under Medicare Part D. Patient adherence to statins was assessed by calculating medication possession ratio (MPR). The results showed that mean patient MPR increased from 75.71 percent under Medicaid to 79.37 percent under Medicare. Results from generalized estimating equations showed that odds of being adherent (i.e., MPR ≥ 80 percent) to statins increased by 36 percent when patients were covered under Medicare Part D. Linear mixed model analysis showed that MPR increased by 3.66 percent when patients were covered under Medicare Part D compared to Medicaid. Also, patient MPR was found to increase by 0.13 percent when patient out-of-pocket payment increased by $1.00. Patient persistence was calculated by measuring gaps in therapy and patients with a gap of 60 or more days were considered to have discontinued therapy. Patients were found to be persistent to their drug therapy for an average of 151.76 days under Medicaid and 159.75 days under Medicare. Linear mixed model analysis showed that patient persistence increased by 7.99 days when patients were enrolled under Medicare Part D compared to Medicaid. Days of persistence was also found to increase by 0.41 days when patient out-of-pocket costs increased by $1.00. Mean number of gap days per claim during the Medicaid period was 11.91 days and decreased to 8.38 days during the Medicare period. Linear mixed model analysis showed that mean number of gap days per claim decreased by 3.52 days when patients were enrolled under Medicare Part D compared to Medicaid. Mean number of gap days in therapy were found to decrease by 0.10 days when patient out-of-pocket costs increased by $1.00. The results of this study showed that implementation of Medicare Part D resulted in an increase in MPR and persistence and a decrease in mean number of gap days per claim for Texas dual-eligible beneficiaries. The results also suggest that increased out-of-pocket costs under Medicare Part D may not have had a negative impact on statin drug utilization by dual-eligible beneficiaries in Texas.