Aim: To (i) evaluate the prescribing patterns of metformin in patients with type 2 diabetes mellitus (T2DM) and determine the prevalence of contraindications to its use, especially renal impairment, and (ii) identify potential cases of lactic acidosis (LA) related to metformin usage.
Method: This retrospective study reviewed all patients with a diagnosis of T2DM and taking metformin who was admitted to a major teaching hospital over an 8-month period. Data including demographics, medical conditions, medications at admission and discharge, and relevant pathology results were extracted from medical records.
Results: A total of 301 patients (209 medical patients, 92 surgical patients) taking metformin were included. According to guidelines, approximately 31% and 21% of patients received metformin inappropriately (in the presence of contraindications or in excessive dosage) at admission and discharge, respectively. At admission, 65 patients (n = 301, 21.6%) on metformin had at least one contraindication to its use, and 42 patients (n = 254, 16.5%) were prescribed an excessive dosage according to their renal function. At discharge, 43 patients (n = 301, 14.3%) continued on metformin with at least one contraindication and 21 patients (n = 191, 11%) received an excessive dosage according to their renal function. Four patients had evidence of LA (plasma lactate concentration > 5.0 mmol/L and pH < 7.35) without clinical diagnosis.
Conclusion: Metformin was often used in patients with contraindications to its use, or in higher than recommended dosages. Reconsideration of the official prescribing information for metformin may be warranted as the risk of harm appears to be very low.
Keywords: contraindication; inappropriate usage; metformin; renal function; type 2 diabetes mellitus.
© 2014 The Authors; Internal Medicine Journal © 2014 Royal Australasian College of Physicians.