Metformin-associated lactic acidosis: Bridging pharmacokinetic determinants, metabolic pathways, and clinical outcomes.

Metformin is the first-line oral anti-hyperglycemic agent for the treatment of type 2 diabetes mellitus due to its effectiveness, cost-efficiency, and acceptable safety profile. Although metformin possesses a favorable safety profile, a rare but serious adverse event known as metformin-associated lactic acidosis (MALA) may occur, particularly in patients with impaired renal clearance or predisposing comorbidities that favor drug retention. High anion-gap metabolic acidosis, increased concentrations of lactate (>5 mmol/L), and arterial pH of less than 7.35 are the hallmarks of MALA. MALA has a multifactorial pathophysiology, driven primarily by mitochondrial complex I inhibition, leading to an altered intracellular redox state and decreased hepatic lactate clearance. Crucially, MALA is fundamentally an accumulation disorder precipitated by an acute decline in kidney function rather than an intrinsic toxicity of metformin at therapeutic concentrations. Many precipitating factors, including acute kidney injury (AKI), chronic kidney disease (CKD), hepatic impairment, sepsis, hypoxia, and dehydration, substantially predispose individuals to this complication. Early identification of clinical signs, such as metabolic acidosis, tachypnea, hypotension, and altered mental status, is essential to a better patient outcome. Diagnostic assessment is based on arterial blood gas values, serum lactate, and renal function tests. Management aims at stopping metformin immediately, providing supportive care, and eliminating the medication through renal replacement therapy (RRT) in severe instances. Prevention measures focus on appropriate patient selection, renal monitoring, dose adjustment, and proactive temporary drug withdrawal during acute intercurrent illnesses ("sick-day rules"). MALA is not highly prevalent, and contemporary evidence demonstrates that mortality is highly context-dependent, with prompt extracorporeal interventions yielding robust survival rates.