Safety of Continuing Metformin in Diabetic Patients With Normal Kidney Function Receiving Contrast Media

Although metformin is not directly nephrotoxic, it has been postulated that can impair gluconeogenesis from lactate, which may lead to lactate accumulation under circumstances such as acute renal failure. In diabetic patients receiving metformin, this condition can be encountered in the setting of acute renal failure following contrast media administration, during coronary angiography i.e. contrast-induced nephropathy. As a result, it has been a part of routine clinical practice to discontinue metformin before angiography to prevent metformin-associated lactic acidosis (MALA). However, there is no general consensus regarding the incidence of MALA and evidence for such intervention is poor. On the other hand, discontinuation of metformin can be associated with detrimental effects on glycemic control and thereby may increase cardiovascular risk in diabetic patients undergoing percutaneous coronary interventions. Consequently, questions have been raised recently regarding the routine discontinuation of metformin, in low-risk patients undergoing coronary angiography.

The present study was designed to assess the role of metformin in lactate production in a group of diabetic patients with normal renal function; and to address the questions about significance of routine discontinuation of metformin in low risk patients undergoing coronary angiography.

Iodixanol will be the only contrast media in all patients, because of its low nephrotoxicity. Serum blood urea nitrogen and creatinin; as well as arterial blood gases will be evaluated prior to angiography, and repeated 24 and 48 hours after the procedure. Glomerular filtration rate (GFR) is calculated using Cockcroft-Gault formula {GFR= 0.85 (for women)}.

Contrast-induced acute kidney injury is defined as a 25-50% or 0.3-0.5 mg/dl net increase in creatinine concentration compared to the baseline values. Metformin-associated lactic acidosis (MALA) is defined as an arterial pH (potential of hydrogen)<7.35 and plasma lactate concentration >5 mmol⁄L. In the M (-) group metformin will re-started 48 hours after angiography, albeit in the absence of evidence of lactic acidosis and GFR of >60 mL/min per 1.73 m2.

A written informed consent is taken from all participants and institutional review board has already approved the trial.

Inclusion criteria

• Diabetic patients receiving metformin who were scheduled for:

• coronary angiography
• coronary angioplasty

Exclusion criteria

• Patients who had contraindication for metformin administration, such as:

• decompensated heart failure
• severe liver disease
• severe hypoxemia
• GFR<60 mL/min per 1.73 m2