Adherence to "-blocker Therapy Under Drug Cost-sharing in Patients With and Without Acute Myocardial Infarction

Published Online: August 01, 2007
Sebastian Schneeweiss MD, ScD; Amanda R. Patrick, MS; Malcolm Maclure, ScD; Colin R. Dormuth, ScD; and Robert J. Glynn, PhD, ScD

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.

  • We confirmed that adherence to b-blocker therapy is decreasing quickly after initiation and the proportion of patients starting b-blockers is still less than optimal after an acute MI.
  • Fixed patient co-payment and co-insurance policies had little negative effect on adherence to relatively inexpensive b-blocker therapy, or the initiation of b-blockers after acute MI.
Spending for prescription drugs in the United States reached more than $200 billion or 12% of all healthcare expenditures in 2004 and has been one of the fastest growing components of healthcare spending.1,2 Medicare Part D drug coverage will bring long-needed improvements in access to prescription drugs but is likely to increase these expenditures further.

In the first months of Part D, seniors were offered 1429 stand-alone drug plans3 that were regulated and overseen by the Centers for Medicare & Medicaid Services.4 These plans had many formularies with a wide range of patient cost sharing,3 few of which have been rigorously evaluated regarding their clinical and economic outcomes. Well-designed patient cost-sharing policies5-8 as well as coverage restrictions9 have been shown to produce net savings from the health plan's perspective10 without adversely affecting health outcomes. Other interventions that disregard clinical logic (eg, global physician budgets, prescription caps) can lead to unanticipated outcomes, including increased rates of hospitalization11 and nursing home admissions.12 The evidence is inconclusive for the common 3-tiered copayment systems.13,14 Generally these studies are criticized for their lack of generalizability because they were conducted in a wide range of patient populations and health systems. A direct comparison of several drug policies in a single system has not been published.

ß-Adrenergic receptor blockers (ß-blockers) are indicated for the treatment of hypertension15,16 and have been shown to be as efficacious as calcium channel blockers17 and angiotensin-converting enzyme inhibitors17-20 in reducing blood pressure and cardiovascular risk. Oral ß-blockers are further indicated for long-term use in all patients recovering from acute myocardial infarction (MI).21,22 Health plan performance measures like the Health Plan Employer Data and Information Set recommend ß-blocker therapy after acute MI in patients who have no contraindications.23 ß-Blockers treat a largely asymptomatic condition (hypertension) and may lead to side effects including fatigue, erectile dysfunction, and dizziness. Not surprisingly, adherence to antihypertensive treatment was less than 50% in elderly patients after 1 year, and only 20% of patients were sufficiently compliant to obtain the therapeutic benefits observed in clinical trials.24 Adherence was further reduced when ß-blockers were combined with statin therapy.25 The rate of initiation of ß-blocker therapy after acute MI was found to be less than 21% in a US Medicare population between 1987 and 1992.26

Spending for ß-blockers was $2.1 billion among US seniors in 2001 according to an analysis of the Medical Expenditures Panel Survey.27 However, despite the fact that the efficacy of ß-blockers has been proven, they are used in too few patients and with disappointing adherence even in the absence of cost sharing, which makes them a problematic target for any cost-sharing policy.

PharmaCare, the province-funded drug insurance plan in British Columbia, provided full prescription drug coverage for all elderly persons before January 2002. In January 2002, a prescription copayment policy for elderly residents of Can$25 (Can$10 for low-income seniors) was implemented. In May 2003, the seniors' copayment was replaced with a 25% coinsurance payment plus an income-based deductible policy. Linking deductible cost-sharing levels to income was intended to prevent low-income patients from underutilizing essential drugs.28,29

This natural experiment among all elderly British Columbia residents provided the opportunity to evaluate the consequences of 2 subsequent patient cost-sharing interventions on adherence to ß-blocker therapy among patients who initiated this therapy and on the initiation of ß-blocker therapy after acute MI in a large, stable population of older adults.



To evaluate the effects of the copayment and coinsurance policies on ß-blocker adherence rates among new users of ß-blockers, we selected 3 cohorts, including a baseline cohort of seniors initiating ß-blocker therapy within 6 months before January 2001, a copayment cohort of seniors initiating ß-blocker therapy within 6 months before the copayment policy in January 2002, and a coinsurance cohort initiating ß-blocker therapy within 6 months before the coinsurance policy in May 2003 (Figure 1). To be eligible for any of the 3 cohorts, patients had to be beneficiaries of the provincial healthcare system during the respective 6-month periods. Initiation was defined as filling a first ß-blocker prescription during the 6-month cohort entry period without having filled a ß-blocker prescription in the 6 months before the initiation date. We required evidence of hypertension as indicated by a diagnosis of hypertension (International Classification of Diseases, Ninth Revision [ICD-9] codes 401.x-404.x) recorded during an office visit or as a hospital discharge diagnosis during the 6 months before initiation date. Follow-up included up to 6 months during the cohort entry phase, depending on when patients initiated ß-blocker use, and an additional 9 months after the policy changes or the respective dates in the control group (Figure 1).

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.

Patient Characteristics

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