Metformin and patients on dialysis.

Abstract

I enjoyed reading the concise, well-referenced summary on prescribing for patients on dialysis.1 However, the statement ‘Metformin is contraindicated due to the risk of lactic acidosis’ is not referenced and is perhaps not supported by the available evidence. A Cochrane review on the risk of fatal and nonfatal lactic acidosis with metformin use in type 2 diabetes concluded that there is no evidence at present that metformin is associated with an increased risk for lactic acidosis when prescribed under the study conditions.2 The authors commented that of the 334 prospective studies, 143 (53%) allowed for the inclusion of renal insufficiency, following 37 360 patient-years of metformin use. One trial in the review questioned the standard contraindications by studying 393 patients, all with at least one contraindication to metformin use, and found no cases of lactic acidosis over four years.3 All of the patients had renal insufficiency, with mean plasma creatinine concentrations of 1.5–2.5 mg/dL (mean 1.8 mg/dL). A review of metformin in chronic kidney disease nicely summarises the issue.4 It cites two small studies of metformin use in dialysis patients and recommends 250 mg daily for peritoneal dialysis patients and 500 mg after each dialysis session for those receiving haemodialysis. Metformin is renally excreted and in overdose has been seen to cause lactic acidosis without other contributory comorbidity. While there are grounds for caution in patients on dialysis, an increased risk of lactic acidosis has not been specifically established. Many renal physicians choose to administer metformin in reduced doses to selected patients with end-stage renal disease because of its proven efficacy in the management of overweight patients with type 2 diabetes.