Secondary failure of glycemic control for patients adding thiazolidinedione or sulfonylurea therapy to a metformin regimen.

OBJECTIVE To assess glycemic control and secondary failure in patients adding thiazolidinedione or sulfonylurea therapy to a metformin regimen in a managed care setting. STUDY DESIGN Retrospective cohort study using administrative claims data. METHODS Participants (mean age, 51.1 years; 55.4% female) were required to have at least 1 prescription claim for a sulfonylurea (n = 300) or a thiazolidinedione (n = 279) between January 1, 2001, and March 31, 2004, as well as metformin use during the prior 6 months and continued metformin use. Secondary failure was measured for patients who initially achieved a glycosylated hemoglobin (A1C) level of less than 7.0% and was defined as a subsequent A1C level of at least 7.0%. RESULTS The mean baseline A1C level was 8.2% and was higher for the patients receiving a combination of metformin and sulfonylurea (A1C level, 8.4%) compared with patients receiving a combination of metformin and thiazolidinedione (A1C level, 8.0%) (P < .05). Overall, 77.7% of patients had a baseline A1C level of at least 7.0%. The mean A1C level decreased by 1.2 (to 7.0%), and 65.1% of patients with a baseline A1C level of at least 7.0% reached goal A1C level. Therapy intensification via addition of another antihyperglycemic agent occurred in 60.7% of study patients. Approximately 2 in 5 patients (41.5%) who initially achieved goal A1C level experienced secondary failure; the mean time to failure was 1.3 years. CONCLUSION Although most patients failing metformin monotherapy reached goal A1C level after addition of a sulfonylurea or a thiazolidinedione, 41.5% of patients observed for up to 4 years who initially attained goal A1C level experienced secondary failure.