Objective: Metformin is a key diabetes therapy. The product information in MIMS states that metformin is contraindicated if the estimated glomerular filtration rate (eGFR) is below 60 mL/min/1.73 m2. The aim of this survey was to determine the doses of metformin prescribed in Australia by Endocrinologists and Endocrine Advanced Trainees.
Design, setting and participants: We invited (via email and newsletters from the Endocrine Society of Australia) Endocrinologists and Endocrine Advanced Trainees to complete a short online survey regarding their use of extended release metformin. We assessed the dose prescribed at various degrees of renal function.
Results: In total, 115 completed the survey. Of those, all would use metformin in patients with type 2 diabetes. However, use of metformin was dependent on renal function. Respondents reported a mean maximal dose of 1991 mg (range 1000 to 2500 mg) of extended-release metformin in patients with an eGFR of > 90 mL/min/1.73m2. Almost all (97%) of respondents reported that they would use metformin in patients with an eGFR of 50 mL/min/1.73m2, with a mean maximal dose of 1450 mg (range 50 to 2500 mg). Seventy-four respondents (64%) indicated that they would use metformin in patients with eGFR of 35 mL/min/1.73m2, with mean maximal dose 913 mg (range 500 to 2000 mg). In patients with eGFR of < 20 mL/min, 7% (n=8) reported that they would still use metformin (mean maximal dose 688 mg, range 500 to 1000 mg).
Conclusion: The use of metformin remains very varied among Endocrinologists and Endocrine Advanced Trainees. Almost all of the respondents would use metformin in patients with an eGFR < 60 mL/min/1.73m2. Current practice, supported by the low incidence of lactic acidosis in metformin-treated patients, indicates that prescribing guidelines may require review.