BACKGROUND: Adherence to prescribed medications is known to help control the effects of high blood pressure. Measurement of medication adherence has been difficult due to lack of data sources that capture whether an individual took medication as prescribed. The CDC 1305 program suggests using the proportion of days covered (PDC) method to calculate medication adherence from pharmacy claims data. The purpose of this analysis is to calculate a statewide baseline for hypertension medication adherence using the PDC method and evaluate the usefulness of Maine’s All-Payer Claims Database (APCD) for this measure.
METHODS: We examined adherence among adults ages 18-85 who filled two or more prescription claims for renin angiotensin system antagonists (RASA medications) and were treated over 90 days during 2015. The 1305 CDC performance measure for hypertension medication adherence is defined as having a PDC of ≥ 80% (having medication for ≥ 80% of total enrollment days). Pharmacy claims were exclusively used to determine medication adherence stratified by sex, age, insurance, rurality, county, and public health district.
RESULTS: 111,104 patients met the analysis criteria (age, enrollment period, and number of prescriptions) based on examining RASA pharmacy claims in the 2015 APCD. Among the 111,104 patients, 92,740 (83.5%) were adherent (PDC ≥ 80%). No notable differences were found by sex or rural-urban status, but medication adherence increased with age. Medicaid beneficiaries were less likely to be adherent (75.9%) than private insurance beneficiaries (84.7%). Rates by county ranged from 81.7% to 85.3% and counties in central Maine were lower than the state average.
CONCLUSIONS: Using pharmacy claims data from Maine’s APCD, we found that 83.5% of Maine adults taking RASAs were adherent. A recent analysis using similar methods found that 79.8% of U.S. Medicare Part D beneficiaries on RASAs were adherent in 2014. We found the major limitation of the APCD is that not all payers are required to report pharmacy claims. Medicaid is required to report all pharmacy claims to the APCD, but private payers are not. Differences in adherence by insurance type may be due to differences in reporting requirements. Complementary data sources would be required to understand adherence for people insured by Medicare, VA, and IHS. This PDC analysis uses pharmacy claims only and is limited to one class of medication that is most exclusively used for hypertension. These analyses do not indicate why patients are non-adherent to medication. Future work will include analysis of anti-diabetic medication adherence.