Impact of Race on Cumulative Exposure to Antihypertensive Medications in Dialysis

Racial minorities typically have less exposure than non-minorities to antihypertensive medications, as has been noted across an array of cardiovascular conditions in the general population.1–10 Even in environments in which there is “universal” access to care, such as the US Veterans Administration system (a healthcare system for which all United States military veterans are eligible, regardless of socioeconomic status)11,12 or state Medicaid programs in the United States (which provide financial assistance with prescription drug costs for socioeconomically disadvantaged persons),13 minorities have lower rates of treatment for cardiovascular disorders. Although race-based differences in care have been noted in the chronic dialysis environment for the creation of arteriovenous fistulas14–16 and outcomes after renal transplantation,17,18 there is little understanding of whether chronic dialysis patients face the same race-based differences in exposure to antihypertensive medications as does the general population. Patients undergoing chronic dialysis have high rates of cardiovascular disease19 and are frequently treated with antihypertensive agents that have demonstrated cardioprotective properties in other populations20–32 or in animal models,33,34 such as angiotensin converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), β-adrenergic antagonists (β-blockers), and calcium-channel blockers (CCBs). Our previous work in the dually Medicaid-and-Medicare–eligible dialysis population showed, perhaps paradoxically, that non-Caucasians are treated with these classes of antihypertensive agents at higher rates than are Caucasians when a cross-sectional approach is used,35 but to date, the cumulative exposure of these groups to these medications over the course of time has not been specifically investigated. To study this issue in detail, we created a novel linkage of data from the United States Renal Data System (USRDS), which contains Medicare claims data in chronic dialysis patients, with Medicaid prescription claims data,35 to create a large cohort of incident dialysis patients who, by virtue of their geographic diversity, are subject to a wide spectrum of policies, procedures, and cultures of care. Chronic dialysis patients who have dual eligibility for Medicare and Medicaid, and who are therefore indigent, constitute a uniquely informative population in which to study how prescribing patterns vary by race, because: (i) such patients have ready access to care and prescription medications via these two public programs, and (ii) chronic dialysis is a setting in which all patients have similarly frequent contact with health care providers. We determined the percentage of time that patients had exposure to ACEIs or ARBs or both, β-blockers, and CCBs. The term “exposure” was deliberately selected because a filled prescription cannot be used to infer either “use” (which suggests proof of ingestion), or adherence (which implies a volitional action by a patient to take a drug as prescribed). To confine our analysis to individuals who were judged suitable candidates for a drug, we deliberately modeled only individuals who received at least one prescription for these antihypertensive agents. Given the importance of studying the way in which race influences care,36 we reasoned that if race is associated with differential exposure to medication over time, further work would be imperative to understand the factors that undermine or facilitate exposure.