The effect of reduced drug copayments on adherence to oral diabetes medications among childless adults in Wisconsin medicaid

Abstract

BACKGROUND: Medication adherence is an indicator of the quality of drug use, which is associated with better health outcomes and reduced health care expenditures. Drug cost sharing can be a barrier to adherence, especially for low-income individuals with chronic conditions. Most of the existing studies in a Medicaid population have evaluated the effects of increasing drug copayments, but few studies have evaluated the effects of reducing drug copayments on medication adherence. Medicaid coverage for low-income childless adults in Wisconsin was expanded on April 1, 2014, which included reductions in drug copayments and monthly caps on out-of-pocket spending. OBJECTIVE: To evaluate changes in adherence to oral diabetes medications using proportion of days covered (PDC) among Medicaid childless adults with type 2 diabetes after the 2014 Medicaid drug copayment reduction. METHODS: A difference-in-differences design was used to compare the changes in medication adherence between childless adults (treatment group) and parents/caretakers (control group). Wisconsin Medicaid's administrative enrollment records, pharmacy claims, and medical claims data were analyzed. Medication adherence was evaluated for 4 commonly used oral diabetes drug classes (i.e., biguanides, sulfonylureas, dipeptidyl peptidase-IV inhibitors, and thiazolidinediones) by adapting the medication adherence quality measures endorsed by the Pharmacy Quality Alliance. The PDC for all diabetes drugs was calculated among patients who filled ≥ 2 prescriptions for any of the 4 drug classes. PDC for each drug class was also measured among patients who had ≥ 2 drug fills for each drug class. The proportion of adherent patients was evaluated using a threshold of PDC ≥ 0.80. RESULTS: Average PDC for all diabetes drugs was 0.87 in the childless adults at baseline and significantly increased by 0.02 (P = 0.025) relative to the parents/caretakers after the copayment reduction. The baseline proportion of adherent patients (PDC ≥ 0.80) among the childless adults was 76% and significantly increased by 6.2 percentage points (P = 0.003) relative to the control group. The odds of adherence to oral antidiabetic drugs increased by 47%, resulting in the proportion of adherent patients in the childless adults group reaching almost 80% after the coverage expansion. In the per class analyses, a significant effect was found for biguanides; the proportion of adherent patients increased by 5.5 percentage points in childless adults compared with the control group (P = 0.022). CONCLUSIONS: This program evaluation found that a reduction of drug copayments in Wisconsin Medicaid improved the quality of medication use by increasing adherence to oral antidiabetic drugs among childless adults.