Date of Award


Degree Type


Degree Name

Doctor of Philosophy in Pharmaceutical Sciences


Interdepartmental Program

First Advisor

Stephen Kogut


Background: Patients with diabetes mellitus often take prescription medications throughout their lives to maintain glycemic control and/or treat co-morbid conditions such as dyslipidemia. The effect of glycemic control and reductions in lipid levels in the prevention of diabetes-related complications has been demonstrated. However, one important factor affecting the pharmacological management of glycemic control and dyslipidemia is adherence and persistence (i.e., continuous use) with treatment. Objective: The objective of this research was to 1) use measurements of medication availability, gaps in therapy, and surplus medication to assess adherence with sulfonylurea medications, evaluate the relationship between these measures, and examine patient- and medication-related characteristics that may influence adherence with sulfonylureas; 2) evaluate adherence with lipid-lowering medications in patients with diabetes mellitus and examine the effect of patient- and medication-related characteristics on adherence; 3) assess persistence with lipid-lowering medications and evaluate patient- and medication-related characteristics that may influence discontinuation of lipid-lowering treatment in patients with diabetes mellitus. Data Source/Methods: Analyses were performed using pharmacy claims data. The data source provided all prescription claims {288,171 dispensations) between April 27, 1997 and May 16, 1999 for 4,503 patients with diabetes. The cohort for the first study was comprised of patients prescribed sulfonylurea medications while new users of lipid-lowering medications comprised the study population for the other two studies. Adherence was measured by continuous and dichotomous measurements of medication availability, gaps in therapy, and surplus medication while persistence was defined as continuation of therapy with a sufficient quantity of medication to cover the observation period. Regression models were used to analyze the effect of patient-related and medication-related characteristics and adherence and persistence with medications. Results: Sulfonylurea medication was available to patients for an average of 89% of days during a 12-month period. This continuous measure of medication availability correlated with measures of gaps in therapy and surplus medication which showed that on average, patients had 15% of days in which medication was not available and 5% of days with surplus medication during the 12-month study period. Interestingly, rates of adherence were similar whether nine or 12 months of prescription claims were examined, suggesting that an additional three months of data did not add any information to the assessment of medication adherence. None of the patient- or medication-related characteristics in the multivariate regression model significantly influenced adherence with sulfonylureas (F5,987=0.59; p=0.7065). Approximately 66% of patients filled enough lipid-lowering medication prescriptions to cover at least 80% or more days in a nine-month observation period. Adherence differed by the class of lipid-lowering medication prescribed at the index date: patients prescribed statin and non-statin medications had an average Continuous multiple-interval measure of Medication Availability (CMA) of 84.1 % ± 22.3% and 70.0% ± 31 .7%, respectively (p=0.2627). Adherent patients ~80%) were less likely to be prescribed insulin therapy (OR=0.304, 95% Cl=0.114, 0.815, p=0.0180) and more likely to be prescribed statin medications (0R=4.709, 95% Cl=0.996, 22.268, p=0.0506) compared with non-adherent patients. No other study factors significantly influenced adherence with lipid-lowering therapy. Of the 165 patients prescribed statin medications, 74% persisted with treatment over six months, 59% over 12 months, and 46% over 18 months of observation. At six months, 60% of patients persisted with non-statin treatment while only 26% of patients were persistent over 12 and 18 months of observation. Approximately 26% of patients who discontinued treatment did so after the initial dispensing. One in 10 patients switched to another lipid-lowering medication: the majority of switches were to another medication within the same class. Compared with patients prescribed statins, patients prescribed non-statin medications were more than twice as likely to discontinue treatment (HR=2.240; 95% Cl= 1.260, 3.982; p=0.0060). Age, gender, type of health plan, number of concomitantly prescribed medications and antidiabetic medication regimen, were not found to be a significant influence on discontinuation of lipid-lowering therapy. Conclusions: Patients with diabetes obtained less medication than prescribed over six-, nine-, 12- and 18-month periods of observation. Measures of medication availability, gaps in therapy, surplus medication and persistence provide an overall picture of medication adherence. The findings of this research provide insight into sub-optimal adherence and persistence with antidiabetic and lipid-lowering medications among patients with diabetes mellitus. These observations highlight the need for health care providers to establish a partnership with patients to improve adherence and persistence with medications.



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