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Metformin overdose

Metformin overdose. Dr. TS Au PYNEH 16 Feb 2005. Toxicology case presentation. M/56 unemployed and divorced Hx of DM, HT, depression FU in GP Attempted suicide by taking >100 tablets of diabetmin 500 mg (metformin) before 3 pm Suicidal notes written

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Metformin overdose

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  1. Metformin overdose Dr. TS Au PYNEH 16 Feb 2005

  2. Toxicology case presentation • M/56 unemployed and divorced • Hx of DM, HT, depression FU in GP • Attempted suicide by taking >100 tablets of diabetmin 500 mg (metformin) before 3 pm • Suicidal notes written • Developed repeated vomiting and diarrhoea since then • Sent to AED at 18:33

  3. Triage and Ix • BP 198/54 • P 102 /min • SpO2 100% (RA) RR 22/min • Temp 36.4℃ • Hemostix = 13.0 • ECG: sinus rhythm 95/min, normal QRS • P/E: dehydrated

  4. Progress in AED • Given activated charcoal 50 g orally • IV NS 500 ml Q8H • BP/P GCS all along stable • Last BP 160/84, P 78 /min • Medical contacted, suggested admitted to general ward

  5. Arterial blood gases • 1st2nd pH 7.248 7.223 pCO2 4.70 4.44 pO2 14.15 16.11 HCO3 15.0 13.4 BE -11.2 -13.1 Metabolic acidosis with respiratory compensation

  6. Blood tests Anion gap: 144 – 108 – 15 = 21 • ABG: pH 7.248 pCO2 4.70 HCO3 15.0 BE -11.2 • RFT: Na 144 K 4.6 Cl 108 Cr 160 • Glucose 12.4 Anion gap metabolic acidosis Lactate = 9.07 mmol/L (N : 0.3 – 1.3)

  7. Progress • Transferred to ICU after first blood tests • Developed ARF • RFT D1 D3 D9 D15 D17 Cr 160 360 904 152 119 • Put on continuous venovenous haemofiltration (CVVH) • Improving trend for acidosis and RFT

  8. Outcome • Transfer out to general ward on D3 • Continue renal support by HD in medical ward • Cr back to normal on D17 • Psychiatric assessment • Refused psychiatric ward admission • Home on D20

  9. Metformin overdose • Metformin – common biguanide used as an OHA • Mechanism of action: ↓hepatic gluconeogenesis MAJOR + ↑peripheral glucose utilization did not lower blood glucose unless other OHA coingested (sulfonylurea)

  10. Anion gap metabolic acidosis MUDPILES M– methanol U– uraemia D– DKA / AKA / SKA P – paraldehyde / phenformin/ metformin I– isoniazid / iron L– lactate E– ethylene glycol S– salicylate

  11. Toxicity of metformin • Lactic acidosis esp in patients with renal impairment • GI effects: anorexia, vomiting and diarrhoea, abdominal pain • Rarely hypoglycemia • Fulminant GI distress leading to ARF, which↑ lactic acidosis

  12. Management • GI decontamination: activated charcoal for early presentation • Antidote for metabolic acidosis: sodium bicarbonate • Supportive care for refractory acidosis and ARF: Hemodialysis

  13. Learning points • Activated charcoal may not be justified as there may be persistent vomiting • Patient should be admitted to ICU right away • ? Aggressive use of NaHCO3 ? initiated in AED after blood taken

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