Association of Income and Prescription Drug Coverage With Generic Medication Use Among Older Adults With Hypertension

Published Online: October 01, 2006
Alex D. Federman, MD, MPH; Ethan A. Halm, MD, MPH; Carolyn Zhu, PhD; Tsivia Hochman, MA; and Albert L. Siu, MD, MSPH

Objective: To determine whether low-income seniors and those without prescription drug coverage are more likely to use generic cardiovascular drugs than more affluent and better insured adults.

Study Design: Cross-sectional analysis.

Methods: We used data from the 2001 Medicare Current Beneficiary Survey. Analyses included noninstitutionalized survey respondents over age 65 years with hypertension who used =1 multisource cardiovascular drugs (N = 1710). We examined the association of income and prescription coverage with use of generic versions of multisource drugs from 5 classes: angiotensin-converting enzyme (ACE) inhibitors, ß-adrenergic receptor antagonists (ß-blockers), calcium channel blockers, a1-adrenergic receptor antagonists (a-blockers), and thiazide diuretics.

Results: Rates of generic medication use were 88.5% (ß-blockers); 92.8% (thiazides); 58.7% (calcium channel blockers); 60.7% (ACE inhibitors); and 52.6% (α-blockers). In multivariate analysis of generic medication use aggregated across the 5 drug classes, individuals with incomes below 200% of the federal poverty level were modestly more likely to use generic medications compared with seniors with incomes above 300% the poverty level. Seniors who lacked prescription coverage were more likely to use generics than those who had employer-sponsored coverage, although the association was of marginal statistical significance (relative risk = 1.29, 95% confidence interval = 1.00, 1.60).

Conclusion: Seniors with low incomes or no prescription coverage were only somewhat more likely to use generic cardiovascular drugs than more affluent and insured seniors. These findings suggest that physicians and policy makers may be missing opportunities to reduce costs for Medicare and its economically disadvantaged beneficiaries.

(Am J Manag Care. 2006;12:611-618)


Cost is a major barrier to care for many elderly patients in the United States. Recent studies have demonstrated that up to 41% of low-income seniors avoid filling prescription medications owing to cost.1-3 This behavior has potentially important public health implications, including worse blood glucose control in diabetic patients4 and an increased risk of angina, heart attacks, and strokes among patients with cardiovascular disease.5

Although the new Medicare prescription drug benefit (Part D) has the potential to help older adults realize meaningful savings on prescription medications,6 costs will remain a significant barrier to care for many, including dual-eligible beneficiaries (Medicare-Medicaid beneficiaries), who face mandatory copayments that could limit their access to needed medications.7 In addition, patients may receive prescriptions from their doctors for medications that are not covered by their Part D plans (PDPs). Numerous PDPs coexist in each region—47 in New York State alone. With so many plans available, physicians are not likely to know whether a medication is covered by their patient's PDP when they write a new prescription, as suggested by recent research.8,9

Substituting generic equivalents for brand name drugs is a safe step toward reducing out-of-pocket drug expenditures for patients with Medicare and other types of prescription drug coverage.10,11 It also may ensure that the prescriptions physicians write for patients are covered even when the details of the PDP's formulary are unknown. However, generic agents remain relatively underused,12,13 despite advocacy for their use14 and increasing efforts to promote generic prescribing through modalities such as formularies15 and mandatory generic substitution.16

Previous studies have demonstrated the potential for millions of dollars in savings on prescription drug spending for the Medicaid program12,17 and for managed care populations11 with greater use of generic drugs, but there have been no nationally representative studies of generic medication use by Medicare beneficiaries, and none that focus exclusively on the elderly. Moreover, none have examined the association between generic drug use and patients' income and prescription coverage status. These issues are of great policy and clinical importance because of the potential impact on medication spending by Medicare, Medicare PDPs, and Medicare beneficiaries with Part D coverage. For these reasons, we sought to examine the extent of generic medication use by elderly Medicare beneficiaries and to determine the association of generic use with these beneficiaries' income and prescription drug coverage. Based on the economic theory of demand for healthcare,18 we hypothesized that low-income seniors and those without prescription coverage would use generic equivalents of brand name drugs more frequently than seniors with higher incomes and prescription drug coverage, after taking into account other demographic and health status variables, and the number of prescription drugs used.

We examined generic cardiovascular drug use in a nationally representative sample of elderly Medicare beneficiaries with hypertension. We used hypertension as a model of chronic disease because of its high prevalence in the United States, the wide availability of generic cardiovascular drugs, and the large prescription drug expenditures associated with this condition, estimated at $18.4 billion in 1998.19

METHODS

Data Source

We conducted cross-sectional analyses of data from the 2001 Medicare Current Beneficiary Survey (MCBS), a nationally representative, rotating panel survey of institutionalized and community-dwelling Medicare beneficiaries who are followed for 3 years.20 MCBS staff conduct 12 interviews in the participants' homes over the course of their participation. Response rates for the MCBS average 82% for the initial baseline survey and 71% in the last survey round.

Study Subjects

We included community-dwelling adults who reported a history of hypertension and who used at least 1 multisource cardiovascular drug in 2001. Multisource drugs are agents available in both their original brand name and equivalent generic formulations. To ensure at least 1 year in Medicare, our analyses focused on individuals age 66 years and older. We excluded individuals with end-stage renal disease or fewer than 12 months of Medicare Part B coverage, and those who did not participate in all MCBS survey rounds in 2001.

Outcome Measures

We determined the proportion of individuals who used 1 or more generic cardiovascular drugs during the year. Intraclass substitution of medications may not be appropriate for all patients because of differences in efficacy or side effects. Therefore, we only examined the use of multisource drugs in all analyses. We first examined the use of 1 or more generic cardiovascular drugs from among multisource agents in 5 drug classes. The 5 drug classes included angiotensin-converting enzyme (ACE) inhibitors, ß-adrenergic receptor antagonists (ß-blockers), calcium channel blockers, a1-adrenergic receptor antagonists (a-blockers), and thiazide diuretics (Table 1). We then separately examined use of generics among multisource drugs within each of the 5 drug classes. We used the US Food and Drug Administration (FDA) Orange Book to identify all generic options within each drug class and only categorized drugs as generic if an application for the generic version was approved by the FDA prior to January 1, 2001.21 ß-Blockers and calcium channel blockers included extended-release agents, which we categorized separately from the parent compound.



Data on prescription medication use in the MCBS are collected by self-report and validated by interviewers' inspection of medication containers, pharmacy receipts, or other documentation provided by respondents. Medication names are recorded verbatim and are checked for accuracy by MCBS staff. We coded medications as generic if the generic version was available in 2001 and the generic name was recorded by the interviewer. Medications, including single and combination agents, were coded as brand name if the interviewer recorded the brand name. The medication was coded as generic for cases in which individuals used both generic and brand name versions of the same drug.

Main Independent Variables

Our analyses focused on 2 independent variables: income and prescription coverage. We examined 5 levels of household income (combined income of survey respondent and spouse, if applicable): less than 100% of the federal poverty level, 100% to 149%, 150% to 199%, 200% to 299%, and 300% or more. We categorized prescription drug coverage as employer sponsored, Medicaid, self-purchased plans (Medigap), self-purchased or Medicare HMO plans, other programs (eg, state-sponsored pharmacy assistance programs and charitable programs), Veterans Administration (VA) coverage, or no prescription coverage (traditional fee-for-service Medicare only). Because Medicare beneficiaries may have more than 1 source of drug coverage, we designated prescription drug coverage according to the source of coverage that paid the largest share of each beneficiary's drug costs.

In our analyses we adjusted for additional variables that may influence access to or use of generic or brand name medications. Because the likelihood of using a generic drug may increase with the number of drugs used, we adjusted for the total number of cardiovascular drugs from the 5 drug classes, as well as the total number of medications used outside of the 5 drug classes. Because some physicians express concerns about lesser efficacy and greater risk of side effects with generic medications compared with their brand name versions,22 we also included asthma, coronary artery disease (CAD), congestive heart failure (CHF), and chronic renal insufficiency (CRI) because many hypertension drugs can exacerbate or improve these conditions. Asthma and CAD were determined using survey data (self-report), whereas CHF and CRI were identified through Medicare Part B claims because these conditions were not assessed during interviews. Subjects were considered to have CHF or CRI if these diagnoses were listed on 1 or more outpatient claims (International Classification of Diseases, Ninth Revision, Clinical Modification codes available on request). Health status was represented by the sum of common chronic comorbid illnesses (asthma, osteoarthritis or rheumatoid arthritis, cancer, CAD, CHF, CRI, diabetes, osteoporosis, and stroke, but not hypertension) and a dichotomous variable for general health (poor, fair, or good vs very good or excellent). In addition, we adjusted for variables that might affect attitudes toward or knowledge of generic medications, including age, sex, race, Hispanic ethnicity, and education. Finally, we examined urban residence and census region because access to generic and brand name medications may differ regionally through variations in prescription plan formularies, pharmaceutical advertising, availability of free samples, or provider practice.

Statistical Analysis

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