Toxic dose

In children, no clear toxic dose of metformin has been established, but ingestions of less than 100 mg/kg of metformin are unlikely to be associated with significant poisoning.

In adults with normal kidney function, severe toxicity typically occurs in those who have taken more than 20 g of metformin. Kidney impairment, diabetes and older age increase susceptibility to acute toxicity. Drugs that cause hypotension (eg calcium channel blockers, beta blockers) also potentiate toxicity.

Chronic use of metformin can lead to accumulation and toxicity. The risk of toxicity is higher after a dose increase or if the patient develops kidney impairment or another comorbidity.