Metformin overdose

Dr. TS Au

PYNEH

16 Feb 2005

Toxicology case presentation

M/56 unemployed and divorcedHx of DM, HT, depression FU in GPAttempted suicide by taking >100 tablets of diabetmin 500 mg (metformin) before 3 pmSuicidal notes writtenDeveloped repeated vomiting and diarrhoea since thenSent to AED at 18:33

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

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

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

Blood tests

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:

144 – 108 – 15 = 21

Anion gap metabolic acidosis

Lactate = 9.07 mmol/L

(N : 0.3 – 1.3)

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

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

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)

Anion gap metabolic acidosisMUDPILESM – methanolU – uraemia D – DKA / AKA / SKAP – paraldehyde / phenformin/ metforminI – isoniazid / ironL – lactate E – ethylene glycolS – salicylate

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

Management

GI decontamination: activated charcoal for early presentation

Antidote for metabolic acidosis: sodium bicarbonate

Supportive care for refractory acidosis and ARF: Hemodialysis

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