A review of intentional and accidental metformin overdoses reported to poison control centers over a five-year period found that serious adverse events were rare, though elderly patients appeared to be at greater risk.
A similar study where cases were reported to Texas poison control centers between the years 2000 and 2006 found that ingested doses of more than 5,000 mg were more likely to involve serious medical outcomes in adults.
Survival following intentional overdoses with up to 63,000 mg (63 g) of metformin have been reported in the medical literature. Fatalities following overdose are rare, but do occur.
The most common symptoms following overdose appear to include vomiting, diarrhea, abdominal pain, tachycardia, drowsiness, and, rarely, hypoglycemia or hyperglycemia. Treatment of metformin overdose is generally supportive as there is no specific antidote.
Lactic acidosis is initially treated with sodium bicarbonate, although high doses are not recommended as this may increase intracellular acidosis. Acidosis that does not respond to administration of sodium bicarbonate may require further management with standard hemodialysis or continuous veno-venous hemofiltration.
In addition, due to metformin’s low molecular weight and lack of plasma protein binding, these techniques also have the benefit of efficiently removing metformin from blood plasma, preventing further lactate over-production.
Metfomin may be quantitated in blood, plasma, or serum to monitor therapy, confirm a diagnosis of poisoning in hospitalized patients, or assist in a medicolegal death investigation.
Blood or plasma metformin concentrations are usually in a range of 1–4 mg/L in persons receiving the drug therapeutically, 40–120 mg/L in victims of acute overdosage, and 80–200 mg/L in fatalities.
Chromatographic techniques are commonly employed.
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Last Updated: Feb 21, 2011