Does Medication Adherence Following a Copayment Increase Differ by Disease Burden

Increasing prescription copayments have been associated with reductions in medication adherence (Piette, Heisler, and Wagner 2004a; Piette et al. 2005; Roblin et al. 2005; Goldman, Joyce, and Zheng 2007; Doshi et al. 2009). Patients with chronic illness are likely to skip or discontinue their medications in response to copayment increases (Piette, Heisler, and Wagner 2004a; Soumerai et al. 2006; Maciejewski et al. 2010). Such cost-related nonadherence (CRN) may exacerbate chronic conditions, generate adverse health events, and increase health care utilization (Lichtenberg 1996; Mojtabai and Olfson 2003; Sokol et al. 2005; Zeber et al. 2007; Heisler et al. 2010), and thus counteract health plan attempts to contain overall health care costs. Much of the evidence of copayment impacts on medication adherence reflects an average effect in a population. However, responses to cost-sharing may be heterogeneous within a population, because the potential benefits and risks of medication adherence vary by patient subpopulations (Hayward et al. 2005, 2006). In particular, the patient response to a copayment increase may differ by patients' comorbidity burden and consequences of nonadherence with recommended treatment. High-risk patients may be more likely to remain adherent because they have a greater likelihood of experiencing an adverse event as a result of nonadherence. In a recent study, commercially insured patients with more severe health conditions were more likely to comply with medication regimens and avert hospitalizations and related costs (Encinosa, Bernard, and Dor 2010). If high-risk patients put a higher value in averting future adverse events than low-risk patients, then we would expect high-risk patients to be more adherent than low-risk patients in response to a medication copayment increase (Ellis and Manning 2007). On the other hand, high-risk patients with greater disease severity or greater comorbidity burden may be less likely to remain adherent than low-risk patients because high-risk patients take more medications and a copayment increase creates a greater cumulative financial burden. Assuming a fixed budget constraint, a high-risk patient would have to reduce consumption of other goods more than low-risk patients to maintain the current level of medication adherence at higher prices. Prior studies that examined whether health status moderates the association between cost-sharing and use of health care or medications found mixed results. Prior cross-sectional studies found similar associations between cost-sharing and medication use for low-risk and high-risk patients (Jackson et al. 2004; Goldman, Joyce, and Karaca-Mandic 2006; Schneeweiss et al. 2007a, b). A study of cost-sharing and outpatient service use found that Medicare beneficiaries with worse self-reported health status were less responsive to cost-sharing for outpatient services than beneficiaries with better health status (Remler and Atherly 2003). A study of Medicare beneficiaries found that CRN was unchanged after the introduction of Medicare Part D for beneficiaries with worse self-reported health status or more comorbid conditions, compared with beneficiaries with better health status or fewer chronic conditions (Ellis et al. 2004; Jackson et al. 2004; Goldman, Joyce, and Karaca-Mandic 2006; Schneeweiss et al. 2007a, b; Madden et al. 2008; Yang et al. 2009). This last paper is most similar to this study in which we examine changes in medication adherence associated with a copayment increase in patients with lower and higher comorbidity burdens. Changes in medication adherence in response to copayment changes may also differ by condition. While patients' out-of-pocket medication spending generally differs by chronic condition (Harman et al. 2004), studies have also demonstrated differential impacts of drug copayment increases across medication classes (Goldman et al. 2004; Joyce et al. 2007; Chernew et al. 2008). In this paper, we consider differences between patients with diabetes and patients with hypertension. Diabetes is physiologically more responsive to lifestyle changes in the short term and may lead patients to try and control their disease more by lifestyle than by the use of medications. Diet and exercise, which have generally been known to lower blood sugar within hours or days, are considered the cornerstone for the treatment of diabetes and are often concordantly recommended before institution of medication therapy (Vijan 2010). While diet therapy such as the DASH diet for hypertension can be successful (Obarzanek et al. 2003), it is generally very difficult for patients to transition to this very low-sodium, high-fruit and -vegetable diet (Karanja et al. 1999; Windhauser et al. 1999). Unlike diabetes, lifestyle impacts on hypertension control are subtler and generally take weeks or months to generate a detectable difference. Finally, the burden of comorbid conditions or complications may differ by primary condition. Patients with diabetes tend to have more comorbid conditions, take more medications (Maciejewski et al. 2010), and have higher health care costs (Yu et al. 2003) than patients with hypertension. Thus, a copayment increase results in a greater cumulative financial burden for patients with diabetes than for patients with hypertension. The purpose of this study is to examine whether medication copayment increases impact patients with high-comorbidity burden and low-comorbidity burden differentially. We also examine whether differences in adherence changes between high- and low-comorbidity burden patients vary by chronic condition (diabetes or hypertension). If there is a differential impact by patient disease burden, then adherence effects and policy inferences drawn from the population may fundamentally misrepresent patients whose response differs from the population (Hayward et al. 2005, 2006). If CRN occurs primarily among high-comorbidity patients, then it may be cost-effective to reduce copayments for these individuals following the principles of value-based insurance design (Chernew, Rosen, and Fendrick 2007; Chernew et al. 2008). Copayment policy changes might be structured differently if CRN occurs primarily among low-comorbidity patients. Identifying patients with chronic conditions who might be especially adversely impacted by copayment increases could also suggest targets for interventions to offset the adherence impacts of increased copayments.