The aim of our study was to verify the adherence to metformin treatment by determining its serum levels during a routine outpatient control.
208 patients with type 2 diabetes mellitus from a single tertiary diabetes centre (aged 68.0±8.9 years, HbA1C 56.0±13.4 mmol/mol) using standard or XR (sustained release) form of metformin were included in the study. Blood sampling for metformin was performed during a regular outpatient visit. Hydrophilic interaction chromatography (HILIC) and high resolution mass spectrometry (Q Exactive Plus instrumentation) were used to quantify metformin levels.
In the whole group, mean metformin levels reached 1480.4±1110.0 ng/ml, while not significantly differing between the standard and XR form. Inadequate values (<100 ng/ml) were measured in 6.7% of subjects, whereas in 2.4% metformin was not detected at all. The presence of subtherapeutic levels was not affected by the administration of XR form (6.3 vs. 8.3% for standard vs. XR, n.s.). In 11.0% of patients, metformin was part of a combination preparation with another antidiabetic drug, with none of the subjects showing sub-therapeutic levels. No difference between patients with optimal and sub-therapeutic metformin values was seen in fasting glucose (8.1±2.6 vs. 8.7±3.6 mmol/l, n.s), HbA1C (55.6±13.3 vs. 58.4±14.8 mmol/mol, n.s.) or BMI (30.6±4.7 vs. 31.3±4.4 kg/m2).
In a tertiary diabetes centre the compliance with metformin treatment was greater than 93% and increased with the use of combination preparations, while the XR form was not associated with a higher adherence rate.
Acknowledgements: MZ CR–RVO (IKEM, IC 00023001) and RVO VFN64165.