Why extended release metformin?
I read with interest Dr. Barbieri’s editorial on polycystic ovary syndrome. It left me wondering: Is there a metabolic or pharmacologic reason why you give metformin XR 1,500 mg with dinner instead of 750 mg orally twice per day?
Marcelo Andreoli, MD
Dr. Barbieri responds
I thank Dr. Andreoli for the important clinical question about one-time or multiple dosing of metformin. To improve patient adherence with metformin treatment, I think once-daily dosing at dinner with an extended-release formulation is more convenient than twice-daily dosing with immediate-release metformin. Following ingestion of immediate- or extended-release metformin, peak metformin blood concentrations are achieved after 2 and 7 hours, respectively. 1 There is some evidence that extended-release metformin has fewer gastrointestinal (GI) adverse effects than immediate-release metformin. 2 In one study, the reported rates of GI adverse effects were 29% versus 39% with extended-release and immediate-release formulations, respectively. 2
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