Health Services Research & Development

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2006 HSR&D National Meeting Abstract


1007 — Differential Medication Adherence Among Veterans with Multiple Chronic Illnesses

Author List:
Piette JD (Center for Practice Management and Outcomes Research)
Heisler M (Center for Practice Management and Outcomes Research)
Ganoczy D (Center for Practice Management and Outcomes Research)
McCarthy JF (Center for Practice Management and Outcomes Research)
Valenstein M (Center for Practice Management and Outcomes Research)

Objectives:
We examined the extent to which medication adherence among patients with multiple chronic conditions varies across drugs in their regimen.

Methods:
We identified all VA patients who had prescription medication use in FY02 for each of three chronic conditions: schizophrenia, diabetes, and hypertension (N=1,683). Adherence to each medication type was assessed using medication possession ratios (MPRs), calculated based on refill data. An MPR <.80 was considered a significant adherence problem. Using multi-level logistic models, we examined the impact of medication type on adherence, as well as the impact of other medication characteristics (e.g., average days supplied per refill), health service use, and sociodemographic characteristics.

Results:
Patients’ adherence was only modestly correlated across drug types. In unadjusted analyses, patients were more likely to have poor adherence to their antipsychotic medications (35%) than their hypoglycemic (29%) or antihypertensive drugs (26%; p <.0001). 79% of patients had on average less than a 30 day supply of their antipsychotic medication, while more than half received on average a 60+ days supply of the other two medication types. In initial multivariate models that did not include days supply, patients were less likely to experience adherence problems with hypoglycemic medications (AOR=0.6) and antihypertensive medications (AOR=0.7) than antipsychotics (both p<.0001). However, when the average days supply and other regimen characteristics were controlled, hypoglycemic and antihypertensive drugs were associated with an increased risk of adherence problems, relative to antipsychotics (both AORs = 1.5, p <.0004).

Implications:
Patients with schizophrenia, diabetes, and hypertension varied in their adherence across treatments in their regimen. They were more likely to experience poor adherence for antipsychotic treatments than for often asymptomatic, medical comorbidities. Differential adherence across medication types was explained primarily by the shorter refill intervals for antipsychotic drugs. When refill interval was taken into account, patients’ adherence to their antipsychotic regimens was actually better than to their regimens for diabetes and hypertension.

Impacts:
Clinicians should consider characteristics of medication regimens, including the refill interval, in designing treatment plans that minimize adherence problems. The short refill interval for antipsychotics may contribute to non-adherence to those regimens.