Date of Award

2001

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Pharmaceutical Sciences

Department

Interdepartmental Program

First Advisor

Susan E. Andrade

Abstract

Diabetes mellitus is a highly prevalent condition, afflicting an estimated 6% of the United States adult population. It is also a complex condition to manage. Dietary, exercise, and drug therapies are essential for reducing the risk of various neurologic and vascular diseases related to disease progression. Tight control of blood glucose as achieved through intensive pharmacologic therapy has been shown to decrease the risk of developing several types of diabetic complications. Success in achieving tight blood glucose control is contingent upon adherence to the prescribed hypoglycemic drug regimen , a behavior known to often be sub-optimal. The objectives of this study were a) to describe hypoglycemic drug utilization, and compare drug regimens prescribed and costs among age groups, insurance plans, and by gender; b) to assess adherence to prescribed hypoglycemic therapies, and to explore the association between nonadherence and change in the strength or type of hypoglycemic medication prescribed; and c) to identify the frequency of nonadherence among patients who are prescribed monotherapy with a sulfonylurea or metformin, as compared to the frequency of nonadherence in patients who are prescribed dual therapy with both medications. Analyses were performed using retail pharmacy data. The data provided included over one-quarter-million dispensings to 5056 diabetic patients. From this population, 2901 patients that received at least 2 dispensings for a hypoglycemic medication during a 12-month period were selected for study. Sulfonylureas were the mainstay of treatment for those receiving oral therapy: 82% of patients received a sulfonylurea as monotherapy or in combination with another hypoglycemic medication. The most frequently observed drug regimen was sulfonylurea monotherapy (40.3%); followed by insulin use only (24.9%); dual therapy with sulfonylurea plus metformin (13.9%); and metformin monotherapy (6.96%). Differences in the drug regimen utilized were found among age groups and between genders. Most notably, sulfonylurea monotherapy was prescribed most frequently for patients 65 years of age and older (age 65 years or older: 48.4%; age 50-64: 43.6%; age under 50: 30.8%, p < 0.0001 ). The 12-month cost of hypoglycemic medication dispensed was lowest among patients 65 years of age or older. The medication possession ratio (MPR) was used as an estimate of adherence. Possession of medication was found to be associated with a change in the strength or type of hypoglycemic medication dispensed. Sulfonylurea users who failed to possess medication for at least 80% of days during a four-month period were 41.7% more likely to receive a dispensing for a different strength of medication in subsequent months, as compared with those possessing medication for at least 80% of days (OR 1.42, 95% Cl 1.02 - 1.96). Additionally, among patients receiving either monotherapy with a sulfonylurea or metformin, those possessing medication for at least 80% of days were 36.4% more likely than those possessing at least enough medication for 80% of days to receive a dispensing for a different strength of medication (OR 1.36, 95% Cl 1.019 - 1.83), or for a different strength or type of hypoglycemic medication (OR 1.39, 95% Cl 1.03 - 1.87). This finding was not statistically significant in the smaller sample of patients receiving monotherapy with metformin. Medication possession was also found to be associated with the number of hypoglycemic drugs prescribed. Patients who were prescribed a regimen of dual therapy with a sulfonylurea plus metformin were found to be less likely to possess medication for 80% or 90% of days, as compared with those prescribed monotherapy with either a sulfonylurea or metformin. In multivariate analyses controlling for age and the total number of dispensings, patients receiving dual therapy were more than 3 times more likely to fail to possess medication for at least eighty percent of days (OR 3.14, 95% Cl 2.42 - 4.08), or 90% of days (OR 3.20, 95% Cl 2.49 - 4.11 ). The findings of this pharmacoepidemiologic research provide insight into the drug utilization patterns of diabetic patients. Among patients in this study, the type of drug regimen prescribed differed in frequency among age groups and between genders. The strength and type of hypoglycemic medication utilized was found to change frequently, particularly among patients that were classified as nonadherent. Overall, a substantial percentage of patients were found to be nonadherent with hypoglycemic drug therapy. Patients least frequently adherent to drug therapy included those under 65 years of age and those prescribed dual therapy with a sulfonylurea plus metformin. Presuming that lack of medication possession results in poor glucose control, patients who do not possess medication are at increased risk for diabetic complications.

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