Objective: To evaluate the effects of patient copayment and coinsurance policies on adherence to therapy with ß-adrenergic blocking agents (ß-blockers) and on the rate of initiation of ß-blocker therapy after acute myocardial infarction (MI) in a population-based natural experiment.
Study Design: Three sequential cohorts included British Columbia residents age 66 years and older who initiated ß-blocker therapy during time intervals with full drug coverage (2001), a $10 or $25 copayment (2002), and 25% coinsurance (2003-2004). We used linked data on all prescription drug dispensings, physician services, and hospitalizations. Follow-up of each cohort was 9 months after the policy changes.
Methods: We measured the proportion of subjects in each cohort who were adherent to ß-blocker therapy over time, with adherence defined as having =80% of days covered. We also measured the proportion of patients initiating ß-blocker therapy after acute MI. Policy effects were evaluated using multivariable regression.
Results: Adherence to ß-blocker therapy was marginally reduced as a consequence of the copayment policy (-1.3 percentage points, 95% confidence interval [CI] = -2.5 , -0.04) or the coinsurance policy (-0.8 percentage points, 95% CI = -2.0, 0.3). The proportion of patients initiating ß-blockers after hospitalization for acute MI remained steady at about 61% during the study period, similar to that observed in a control population of elderly Pennsylvania residents with full drug coverage.
Conclusions: Fixed patient copayment and coinsurance policies had little negative effect on adherence to relatively inexpensive ß-blocker therapy, or initiation of ß-blockers after acute MI.
(Am J Manag Care. 2007;13:445-452)
We evaluated the consequences of patient co-payment and co-insurance policies on the adherence to b-blocker therapy and on the rate of initiation of b-blocker therapy after acute myocardial infarction (MI) in a population-based natural experiment.
All patients were identified in the linked healthcare utilization databases of the publicly funded healthcare system of British Columbia. Pharmacists enter medication names, dose, and dispensed quantity for all prescribed drugs into a single database via a province-wide network that ensures minimal underreporting and misclassification.30 This recording is independent of the payer and includes out-of-pocket purchases of prescription medications. The Ministry of Health maintains linkable data on all physician services and hospitalizations for all persons age 65 years and older. Up to 25 diagnoses for hospital discharges and 1 diagnosis for each medical service are recorded, with good specificity and completeness.31
To assess the effects of the policy changes on rates of ß-blocker initiation after MI, we identified all patients who were hospitalized with an acute MI between January 2000 and December 2004, a period spanning the baseline and policy periods. Myocardial infarctions were identified based on the presence of an ICD-9 diagnosis code of 410.x as a primary diagnosis and a length of hospitalization between 3 and 180 days; this definition has been found to be highly accurate (positive predictive value, 95%).32 Patients also were required to survive at least 60 days after hospital discharge. The outcome of interest was ß-blocker initiation within 60 days of discharge. We created identically defined cohorts of elderly patients with a hospitalization for acute MI in Pennsylvania and used their ß-blocker initiation rates to control for any temporal trends that might exist in b-blocker prescribing post-MI. These patients were Medicare beneficiaries and enrolled in the Pennsylvania Pharmaceutical Assistance Contract for the Elderly, a state-funded prescription benefit program for low-income seniors with constant $6 copayment drug coverage throughout the study period.
Study End Points
Adherence was calculated for each calendar month as the proportion of patients days categorized as adherent. First the proportion of days covered (PDC)33 was calculated for each patient by dividing the number of days on which the patient had a ß-blocker supply available by the number of cohort membership days the patient contributed in that calendar month. Based on their PDC, patients were then classified as adherent in that month if their PDC was larger than 0.80, a somewhat arbitrary but widely used threshold.34-36 The numerator of the PDC measure was calculated by creating a ß-blocker supply diary for each patient day by stringing together consecutive ß-blocker dispensings based on dispensing dates and reported “days supply.”37 When a dispensing occurred before the previous prescription should have run out, utilization of the new prescription was assumed to begin the day after the end of the old prescription and days supply were accumulated. If a dispensing caused a patient's accumulated supply to exceed 180 days, accumulated supply was truncated at 180 days. Discontinuation was defined as failing to fill a new ß-blocker prescription within 90 days of exhausting a previous prescription. The discontinuation date was the end of the previous prescription.
The denominator of the PDC measure was the number of days the patient contributed in that calendar month. Residents who left the province or died were censored from the denominator on their date of death or at the end of their enrollment in the British Columbia Medical Services Plan.