Clearance of metformin by hemofiltration in overdose

Metformin is prescribed with an increasing frequency for patients with Type II diabetes mellitus; the increasing availability increases the risk of intentional overdoses. Metformin may cause severe lactic acidosis in overdose, especially when accompanied by co-ingestants or other medical conditions that alter lactate handling or metformin elimination. Though the clearance of therapeutic metformin by hemodialysis is known, the clearance in the setting of a large overdose has not been reported.

A 58-year-old man with a history of Type II diabetes, hypertension, bipolar disease, and decreased renal function presented after ingestion of approximately 40 500-mg metformin tablets and 20 240-mg diltiazem sustained-release tablets. Clinical manifestations of poisoning included somnolence, hypotension, bradycardia, severe lactic acidosis, and ultimately death. Gastric decontamination was attempted with gastric lavage, multiple dose activated charcoal, and whole bowel irrigation. Hemodynamic support was provided with pressors, glucagon, insulin, and intra-aortic balloon pump. Due to hypotension, continuous renal replacement therapy, rather than hemodialysis, was initiated. Continuous veno-venous hemodialysis was performed with a blood flow of 180 mL/min and dialysate flow of 2.5 L/h. A Multiflow 60 kidney (Cobe) on a Prisma (Cobe) continuous renal replacement therapy machine was used. The initial metformin level was 110 microg/mL (therapeutic range 1-2 microg/mL). By continuous veno-venous hemodialysis, an absolute clearance of 50.4 mL/min was obtained.

Metformin was cleared by the continuous veno-venous hemodialysis modality of continuous renal replacement therapy in this metformin overdose. Although a fatal outcome occurred in this patient, its utility in other patients with metformin overdose should be investigated.