OBJECTIVES: Glucophage®XR is a new extended-release formulation of metformin which permits once-daily medication. Clinical studies show that Glucophage®XR demonstrate the same antihyperglycemic efficacy as immediate-release metformin (Glucophage®). However, in a retrospective chart review, patients with type 2 diabetes experienced fewer GI side effects and comparable or better glycemic control, based on HbA1C measurement, when switched from Glucophage® to Glucophage®XR. Mean HbA1c values were 7.8%-points before the switch and 7.5%-points afterwards. The CORE Diabetes Model, a peer-reviewed, validated, model was used to project the long-term cost-effectiveness of switching patients from Glucophage® to Glucophage®XR. METHODS: The CORE Diabetes model employs standard Markov/Monte Carlo simulation techniques to describe the long-term incidence and progression of diabetes-related complications. Transition probabilities were derived from major diabetes studies. Clinical effects of switching from Glucophage® to Glucophage®XR were derived from a retrospective database study. The analysis was performed using published UK-specific costs, health care resource utilization, clinical data and recommended discount rates of 3.5% for costs and clinical outcomes. A lifetime horizon and NHS payer perspective was taken. Only direct costs were considered. Sensitivity analyses were performed. RESULTS: Switching patients from Glucophage® to Glucophage®XR was projected to improve life expectancy by 0.10 years, quality-adjusted life expectancy by 0.09 years, and decrease overall lifetime costs by £201/patient. Results were most sensitive to variations in assumptions about changes in HbA1c when patients are switched from Glucophage® to Glucophage®XR, and the relative costs of treatment. CONCLUSIONS: In real life, due to improved tolerability, compliance, and glycemic control, switching patients from Glucophage® to Glucophage®XR may improve longterm patient outcomes and lead to overall cost savings.