A FLAVELL1, S COHNEY1,2, C NELSON1,2
1Western Health, , Australia, 2The University of Melbourne, , Australia
Background: Metformin is the initial recommended glucose lowering agent in type two diabetes mellitus, and one of the most commonly prescribed medications in Australia. Metformin-associated lactic acidosis (MALA) is an uncommon but feared side effect usually precipitated by acute illness in combination with renal, hepatic or cardiac dysfunction. Inadvertent or intentional drug overdose can also cause MALA and there is limited evidence to guide management of such cases.
Case: A 55-year-old female presented to hospital 6 hours after intentional polypharmacy overdose, which included 132g of extended release metformin. The patient was hypotensive, anuric, and had a lactic acidosis with arterial blood pH 7.18, lactate 12mmol/L, and bicarbonate 14mmol/L. She continued to deteriorate despite high dose vasopressors, intravenous bicarbonate therapy and 5 hours of continuous venous-venous haemodiafiltration (CVVHDF), after which her pH was 6.8, lactate 24mmol/L, and bicarbonate 3mmol/L. CVVHDF was replaced by high flux haemodialysis (HFHDx) using a Polyflux® 210H (Gambro) dialyser, pump speed 300mL/min, dialysate flow 500mL/min and dialysate bicarbonate 40mmol/L. An initial 8 hours of HFHDx led to stabilisation of her biochemical parameters, but she rapidly deteriorated when HFHDx was temporarily withdrawn. HFHDx was continued for a further 27 hours after which the patient biochemically and haemodynamically improved. The patient required intermittent HFHDx support for a further 30 days until renal recovery.
Discussion: This case of severe MALA followed a polypharmacy overdose that included 132g metformin. The resultant refractory lactic acidosis did not improve until institution of 35 hours of continuous HFHDx, which was both more effective than CVVHDF and well tolerated. Prolonged continuous HFHDx should be considered in all cases of severe MALA, particularly those refractory to CVVHDF.
Advanced Trainee in Nephrology