Metformin as secondary therapy in a defined population with type 2 diabetes

This study was undertaken to assess the effect of metformin as a second-line oral antihyperglycemic agent in a defined population with type 2 diabetes mellitus. We measured the extent and circumstances of metformin use in the 15,000-person diabetes registry of a large, group-model health maintenance organization (HMO). Among subsets of patients in whom adequate glycemic control could not be maintained with sulfonylurea (SU) therapy, we compared glycemic control before and after metformin use to glycemic control during a similar interval before metformin was introduced. Metformin users were significantly more likely than nonusers to have had poor glycemic control at baseline. Nearly two thirds (63.8%) of patients with a glycosylated hemoglobin (Hb A1c) level >10% switched to metformin, as did 46.3% of those with an Hb A1c level of 8% to 10%. In all patients (metformin users and nonusers) in whom SU therapy failed to maintain glycemic control, Hb A1c levels decreased 0.9% after metformin was introduced, compared with a decrease of 0.4% during the control period. In a group-model HMO that promoted the use of metformin as second-line therapy in patients unable to maintain glycemic control with SU therapy, metformin reduced hyperglycemic levels.