The Economic Rationale for Adherence in the Treatment of Type 2 Diabetes Mellitus

Patient adherence to prescribed therapies in type 2 diabetes mellitus (T2DM)—including lifestyle changes as well as medications—is an area of enormous importance because of the strong correlations between adherence, patient outcomes, and treatment costs.^1,2 Because diabetes is a chronic condition, long-term adherence to therapy is a necessity, which differs from adherence to short-term therapy for an acute condition (eg, antibiotics, antacids). The topic of adherence to therapy in T2DM is of particular interest to managed care stakeholders because T2DM is a disease that affects a large number of patients and is associated with considerable costs. The relationship between treatment adherence and costs would appear to be intuitive; that is, the economic benefits of achieving better treatment adherence in terms of lower long-term costs would seem to justify the up-front costs of medications and therapeutic strategies that improve adherence. However, the high costs of specific medications, and the costs of implementing certain therapeutic strategies, mean that the use of a given medication or treatment strategy can only be justified from a cost perspective if the incremental improvement in adherence is associated with cost savings greater than the cost of therapy. This article focuses on key factors pertinent to the economic rationale for treatment adherence in T2DM.

The Cost of Diabetes in the United States

According to the American Diabetes Association (ADA), approximately 17.5 million people in the United States had a diabetes diagnosis (type 1 diabetes mellitus [T1DM] or T2DM) in 2007, a large increase from the ADA estimate of 12.1 million in 2002. In addition, approximately 6.6 million people in the United States had diabetes in 2007, and remained undiagnosed.³

The ADA estimates that the total costs related to diabetes in 2007 were $174 billion, $116 billion of which resulted from excess medical costs and $58 billion from lost productivity.³ An analysis of diabetes-related costs, performed by Dall et al, separated out both epidemiological and cost data related to T2DM versus T1DM. They determined that in 2007, 16.5 million of the 17.5 million people in the United States with diabetes had T2DM. Furthermore, they established that T2DM accounted for $159.5 billion of the $174 billion total costs, including medical costs of $105.7 billion and indirect costs of $53.8 billion.⁴ With regard to healthcare expenditures, the ADA data show that approximately half of these costs are attributable to hospitalization and to longer length of stay (LOS) per admission as compared with patients without diabetes. In 2007, outpatient medication and supplies attributable to diabetes cost $27.7 billion, including $3.7 billion for insulin (2.3% of total costs related to T2DM) and $8.6 billion for oral agents (5.4% of total costs related to T2DM).³

Rates of Adherence, Association With Achieving A1C Targets, and Consequences of Poor Glycemic Control

Given the large number of patients impacted by T2DM and the associated cost burden to payers, employers, and patients themselves, there exists a significant opportunity to improve outcomes and reduce costs. One potential target for improving outcomes is patient adherence to prescribed therapy. Improvements in adherence would improve glycemic control, and improvements in glycemic control would help reduce morbidity and mortality related to uncontrolled T2DM.^2,5 Based on data from studies involving patients with diabetes in the United States, every percentage point reduction in glycated hemoglobin (A1C) is associated with a 40% reduction in the risk of microvascular complications such as kidney diseases, eye diseases, and neuropathies.⁶

The management of T2DM necessitates patient adherence to both drug and nondrug therapies. While lifestyle interventions remain an essential component of therapy, as recognized by professional guidelines for the management of T2DM,⁷ this article will focus on the health economic impact of improving adherence to drug therapy.

The ADA recommends an A1C target of less than 7%.⁷ However, a substantial proportion of individuals with diabetes do not achieve this goal. An analysis published in 2009 of data from the National Health and Nutrition Examination Survey (2003-2006) showed that only 57% of adults with diabetes achieved the ADA A1C target of less than 7%.⁸

In the case of drug therapy, adherence is the degree to which a patient takes a medication as prescribed. Methods of measuring adherence include direct methods (eg, observing the patient taking their medication) and indirect methods (eg, asking the patient whether they took their medication; counting pills; reviewing data regarding prescription refills).⁹

The importance of adherence to glycemic control may be seen in the results of a 1-year study of 1560 patients with T2DM which found that A1C was reduced by 0.34% for every 25% increase in medication adherence (P = .0009).⁵ In this study, adherence was assessed during clinic visits; patient-reported medication use was compared with the clinician-recommended medications from the previous visit.⁵ Despite the importance of adherence to glycemic control, there is room for improvement with regard to current levels of adherence. The rate of adherence to oral medications for glycemic control ranges from approximately 65% to 85%, and the rate of adherence to insulin ranges from approximately 60% to 80%. Regimens requiring more frequent dosing tend to have lower adherence rates.¹⁰ The impact of dosing schedule on adherence will be discussed in the other articles in this supplement.^11,12

The potential consequences of poor adherence in terms of healthcare utilization and mortality were demonstrated in a study at Kaiser Permanente of Colorado, which included 11,532 patients with diabetes.⁵ This study found a 21.3% rate of nonadherence to treatment, where nonadherence was defined as filled prescriptions covering less than 80% of the total days during which medication should have been taken. Patients who were nonadherent to treatment had a higher risk of hospitalization and all-cause mortality compared with patients who were adherent (both P <.001).⁵

Cost Implications of Poor Adherence

There are multiple ways to evaluate the impact of treatment adherence on costs in diabetes. Broadly speaking, the available studies fall into 2 categories: a) those that compare levels of treatment adherence with measurable treatment costs and/or healthcare utilization, and b) those that do not necessarily evaluate adherence per se but examine the impact of poor glycemic control on treatment costs and/or healthcare utilization.

Relationship of Treatment Adherence to Costs and Healthcare Utilization