The cost-effectiveness of adding the two health insurance covered thiazolidinediones (TZDs)- rosiglitazone or pioglitazone, to metformin in treating type 2 diabetes mellitus was assessed from a Taiwanese National Health Insurance (NHI) perspective. This analysis was based on patient-level data extracted from Taiwan's NHI databases. Type 2 diabetic patients who received consecutive metformin treatments between 2001 and 2005 were identified. Clinical effectiveness, a proxy of glycemic control (time to insulin dependence), and direct medical cost were also estimated. Incremental cost-effectiveness ratio (ICER) was calculated and expressed as cost per delayed year to insulin dependence. Compared to add-on non-TZDs, add-on rosiglitazone and pioglitazone were associated with delays of additional 151 days (0.41 years) and 101 days (0.28 years) in insulin dependence, respectively. Total mean medical costs were higher in add-on TZDs users compared to add-on non-TZDs users. The additional total medical costs of add-on rosiglitazone or pioglitazone were comparable, with ICERs of 95,874 and 95,485 New Taiwan (NT) dollars per year delay in insulin dependence, respectively. Add-on TZDs improves glycemic control but also increases direct medical cost. In terms of the incremental medical costs associated with these clinical benefits, add-on rosiglitazone or pioglitazone are similar in Taiwan.

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