Metformin overdose

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 gt100 tablets of
  diabetmin 500 mg (metformin) before 3 pm
• Suicidal notes written
• Developed repeated vomiting and diarrhoea since
  then
• Sent to AED at 1833

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

• 1st 2nd
• 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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