Background: Medication adherence, defined as taking medications as prescribed, is a key component in controlling disease progression and managing chronic illnesses such as diabetes, hypertension, and high blood cholesterol. These diseases constitute 3 of the top 5 most prevalent conditions among Medicare beneficiaries, warranting further attention to find ways to promote better medication adherence. The scientific literature has established the clinical and financial benefits of medication adherence and the role of dispensing channel in impacting adherence to medications. However, a common limitation in channel-adherence studies is the failure to control for healthy adherer effect (HAE), referring to individuals who are likely to engage proactively in activities that improve their adherence. Healthier individuals may choose the home-delivery channel to ensure continuity in their medication regimens and to minimize obstacles to adherence, such as inadequate access, inconvenience, and financial concerns. Thus, better medication adherence in home delivery may reflect healthier patients' predisposition to self-select for home delivery options. To accurately attribute the impact of dispensing channel on adherence, research would need to control for bias from a patient's predisposition to be adherent.
Objective: To examine the association of pharmacy dispensing channel (home delivery or retail pharmacy) with medication adherence for Medicare Part D beneficiaries taking medications for diabetes, hypertension, or high blood cholesterol, while controlling for low-income subsidy status, differences in days supply, and prior adherence behavior (PAB) as a way to partly control for HAE.
Methods: A retrospective analysis using de-identified pharmacy claims data from a large national pharmacy benefits manager between October 2010 and December 2012. Continuously eligible Medicare Part D beneficiaries (Medicare Advantage and prescription drug plans participants only) aged 65 years or older who had an antidiabetic, antihypertensive, or antihyperlipidemic prescription claim between October and December 2010, were identified and followed for the next 2 years. Those enrolled in a home delivery auto refill program were excluded from this analysis. Multivariate logistic regression was used to evaluate the impact of dispensing channel on medication adherence, controlling for differences in demographics, low-income subsidy status, disease burden, and drug-use pattern. Patients with a proportion of days covered of ≥ 80% were considered to be adherent. The analysis controlled for PAB by using patients' adherence status in the year 2011.
Results: The final analytical samples consisted of 150,389 diabetic patients, 615,618 hypertension patients, and 358,795 high blood cholesterol patients. The adjusted odds of being adherent for beneficiaries using home delivery were 1.25 times higher (CI = 1.20-1.30) for diabetes medications, 1.29 times higher (CI = 1.27-1.32) for hypertension medications, and 1.26 times higher (CI = 1.23-1.29) for high blood cholesterol medications, compared with beneficiaries using retail channels to obtain their prescriptions. PAB was the strongest contributor to the odds of a patient being adherent across all 3 therapy classes, ranging from odds ratio of 4.48 to 8.09.
Conclusions: After excluding patients who received any prescriptions via home delivery auto refill programs and controlling for PAB, differences in days supply, low-income subsidy status, demographics, and disease burden, Medicare beneficiaries who use home delivery for antidiabetics, antihypertensives, or antihyperlipidemics have a greater likelihood of being adherent than patients who fill their prescriptions at retail. The results of this study provide evidence that where medications are received may impact adherence, even when controlling for PAB. Use of the home delivery dispensing channel may be an effective method to improve adherence for Medicare beneficiaries.