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Metformin Toxicity and the Emerging Role of Methylene Blue By Jordan Glasgow, PharmD, and Megan A. Rech, PharmD, MS, on behalf of the SAEM Academy of Emergency Medicine Pharmacists
SAEM PULSE | JANUARY-FEBRUARY 2026
Background
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Metformin has remained a foundational therapy for type 2 diabetes mellitus since its approval in the United States in 1995 because of its efficacy, safety profile, affordability, and broad metabolic benefits. Although its overall riskbenefit ratio is favorable, metformin toxicity—most notably metformininduced lactic acidosis (MILA) and metformin-associated lactic acidosis (MALA)—represents a rare but potentially life-threatening complication. According to the 2023 National Poison Data System Report, metformin combination and singleagent products were mentioned
in approximately 10,000 cases, with 12.8% requiring hospital management. Mortality rates rise significantly when severe acidosis develops, underscoring the importance of prompt recognition, early supportive care, and consideration of adjunctive therapies such as methylene blue when conventional measures are insufficient. In this column, we outline the pathophysiology, clinical presentation, and management of metformin toxicity.
Pathophysiology
Metformin is a hydrophilic biguanide transported intracellularly through organic cation transporter 1 (OCT1), which is predominantly expressed
in hepatocytes. Therapeutically, metformin lowers blood glucose by inhibiting hepatic gluconeogenesis, a mechanism mediated by inhibition of mitochondrial respiratory chain complex I. This process reduces adenosine triphosphate (ATP) production and increases adenosine monophosphate (AMP) levels. Elevated AMP activates AMPactivated protein kinase, increasing nitric oxide (NO) production. Metformin also inhibits pyruvate carboxylase flux, diverting pyruvate toward lactate formation. Toxicity results from the combination of impaired oxidative phosphorylation, increased anaerobic metabolism, and reduced