A ???Real-World??? Analysis of Persistence on and Adherence to Glipizide GITS, Glipizide IR and Glibenclamide in Managed Care among Patients with Type 2 Diabetes Mellitus

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Abstract
This study compared persistence on and adherence to therapy with glipizide gastrointestinal therapeutic system (GITS), glipizide immediate release (IR) and glibenclamide (glyburide) in commercially insured patients newly treated for type 2 diabetes mellitus. The objective of the study was to determine if there were differences in persistence and adherence between the three second-generation sulphonylureas. This was a retrospective longitudinal claims data analysis for commercial enrollees in eight independent practice model health plans. Study subjects were 25 years of age or older with a first prescription for a study drug from 1 January 1996 through 31 December 1999. All subjects were newly treated with medication for diabetes mellitus, and were initiated on monotherapy. To be included in the study, subjects had to be continuously enrolled in their health plan 6 months prior to their index claim and at least 30 days following the index claim. Persistence was defined as the total days from the index prescription fill date until termination, switch or augmentation of therapy. Adherence was defined as the ratio of days supplied to total days in the treatment period. The treatment period for the measurement of adherence was defined as the period from index prescription fill date to run-out of days supplied of the last filled prescription for the index drug. Cox proportional hazards analysis was used to compare differences in persistence, and multivariate regression was used to assess differences in adherence. Of the 24 311 subjects, 35% filled a first prescription for glipizide GITS, 15% for glipizide IR, and 50% for glibenclamide. Over one-half of study subjects were male, and the average age was between 51 years for the glipizide GITS cohort and 53 years for the glibenclamide cohort. By the end of the study, 79% of subjects had terminated therapy with their index drug. Cox proportional hazards analysis showed that patients taking glipizide IR were 1.33 times more likely to experience treatment change [95% confidence interval (CI) 1.25 to 1.42], and patients taking glibenclamide were 1.16 times more likely to change therapy (95% CI 1.11 to 1.22) compared with patients taking glipizide GITS in the first 90 days following initiation of therapy. Similar results were found upon subsequent analysis in the 1620 days following the index prescription. The analysis of adherence showed that patients taking glipizide IR or glibenclamide were less adherent to therapy compared with patients taking glipizide GITS (p < 0.001). Glipizide GITS appears to have an advantage in persistence on and adherence to therapy compared with glipizide IR and glibenclamide. These differences may be related to administration frequency. Lack of persistence and adherence has potential clinical and economic consequences.