An in vitro study of metformin adsorption to activated charcoal

Metformin is a biguanide used to manage patients with type 2 diabetes mellitus. However, metabolic acidosis with an elevated lactate concentration and death caused by metformin overdoses are toxicological concerns. Although activated charcoal has been widely used for gastrointestinal decontamination in cases of acute poisoning, there is no evidence regarding its efficacy in treating metformin overdoses. We therefore evaluated the adsorptive capacity of activated charcoal for metformin in vitro.

Activated charcoal (specific surface area: 1,080 m²/g) mixed with various concentrations of metformin solution was dissolved in simulated gastric and intestinal fluids at 37° Celsius. The suspension was then filtered and the metformin concentration in the filtrate was determined using high-performance liquid chromatography. The maximum adsorptive capacity for metformin was calculated using the Langmuir adsorption isotherm equation.

The amount of metformin adsorbed per gram of activated charcoal ranged from 0.7 to 8.1 mg/g at pH 1.2, and from 8.4 to 48.2 mg/g at pH 6.8. The corresponding maximum adsorptive capacities were 10.6 mg/g and 55.9 mg/g respectively.

The maximum adsorptive capacity of activated charcoal for metformin was similar to that of its capacity for other poorly adsorbed substances. This is likely because metformin is water-soluble and has high polarity-factors that correlate with poor adsorption on activated charcoal.

The maximum adsorption of metformin by activated charcoal was low. Therefore, activated charcoal may not be effective for treating patients with metformin overdose.