The present study aims to evaluate the strict application of the 2018 European Society of Cardiology guidelines on myocardial revascularization, that recommends to check renal function if patients have taken metformin immediately before angiography and withhold metformin if renal function deteriorates.

The aim of this study is to assess the safety of metformin in diabetic patients undergoing coronary angiography in terms of risk of lactic acidosis and to individuate eventual predictors of augmented lactate after coronary angiography.

The study is designed as an open-label (both physician and participant know that metformin will not be discontinued before PCI and in the following 48 hours), prospective, single arm study.

In our historical cohort of diabetic patients taking metformin, we observed a mean value of lactate of 1.2+0.7 mmol/l.

A total of 150 patients will be enrolled. Patients with any deviations from the study protocol will be enrolled in a parallel observational registry.

The study consists of a screening phase, a 30-day observational phase, and an end-of-follow-up visit or phone interview. The total duration of participation in the study for each participant is approximately 30 days.

Inclusion Criteria:

• Diabetic patients treated with metformin undergoing coronary angiography.

Exclusion Criteria:

• Known coronary anatomy with planned complex percutaneous coronary intervention with high probability of large amount of contrast use (3.7 * estimated glomerular filtration rate; e.g.: 167 ml in a patients with an eGFR of 45 ml/min/1.73m2).
• Moderate to severe impairment of renal function (eGFR<45 ml/min).
• Moderate to severe impairment of liver function (Child-Pugh class B or C).
• Severely impaired left ventricular ejection fraction (LVEF <35%).
• Patients undergoing primary percutaneous coronary intervention (i.e., patients presenting with ST elevation myocardial infarction).
• Severe to very severe chronic obstructive pulmonary disease (GOLD class 3 to 4).
• Patients scheduled for cardiac surgery in the following 5 days.
• Inability to provide informed consent.

The data that support the findings of this study will be available from the corresponding author on reasonable request.