Incidence and risk factors for hyperlactatemia in ED patients with acute metformin overdose

The goals of this study are to describe clinical characteristics and risk factors for metabolic acidosis with hyperlactatemia in emergency department (ED) patients with acute metformin overdose.

This was a secondary analysis of data from a retrospective observational cohort of adult ED patients presenting with acute drug overdose at two tertiary care hospitals over 5 years. The primary outcomes were: (1) hyperlactatemia, defined as a lactate concentration ≥ 2 mmol/L at any point during hospital admission and, (2) metformin associated lactic acidosis (MALA), defined as a lactate concentration ≥ 5 mmol/L and pH <7.35 at any point during hospital admission.

We screened 3739 acute overdoses; 2872 met eligibility, 56 self-reported metformin overdose (57% female, mean age 55.8). Of these, 39 had measured lactate values. There was a high incidence of hyperlactatemia (56.4%); MALA was less frequent (17.9%). There were no deaths. Low serum bicarbonate was an independent clinical risk factor for hyperlactatemia (adjusted p < 0.05). Acetaminophen co-exposure was an independent clinical risk factor for MALA (OR 24.40, 95% CI 1.6-376.4).

In ED patients with acute metformin overdose, initial hyperlactatemia is common but MALA is unusual. Acetaminophen co-exposure is a novel independent risk factor for the occurrence of MALA that deserves further investigation.