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Metformin-associated lactic acidosis (MALA) involves mitochondrial Complex I inhibition, traditionally diagnosed via indirect markers. We present platelet high-resolution respirometry (HRR) as a novel "liquid biopsy" to directly quantify metformin-induced systemic bioenergetic lesions. A 65-year-old diabetic male presented with severe lactic acidosis, acute kidney injury, and profound hypoglycemia after intentionally overdosing on metformin (120 g), dapagliflozin (600 mg), and insulin glargine (300 U). While hemodialysis cleared plasma metformin and resolved the acidosis, refractory hypoglycemia required high-dose IV glucose for over six days. Day 2 platelet HRR revealed severe Complex I inhibition despite significantly decreased plasma metformin, indicating a profound "toxicodynamic lag." Mitochondrial bioenergetics recovered by Day 7, reflecting natural platelet turnover. The protracted hypoglycemia was driven by a synergistic triad: metformin-inhibited gluconeogenesis, insulin glargine's prolonged depot effect, and dapagliflozin-induced persistent renal glucose wasting. Platelet HRR has the potential to be a clinically applicable tool to reveal the "hidden" cellular phase of metformin toxicity missed by standard biomarkers. Furthermore, clinicians must anticipate severe, protracted hypoglycemia in mixed overdoses involving SGLT2 inhibitors.