Metformin: safety in cardiac patients

Abstract

Metformin is a biguanide, insulin sensitiser that reduces blood sugar levels. There are concerns about the risk of lactic acidosis in patients receiving metformin who have procedures requiring iodinated contrast, and in those with renal impairment or heart failure. The data on which these concerns are based are reviewed, with the conclusion that metformin treatment is rarely to blame for lactic acidosis. A generic policy of stopping metformin 48 h before and 48 h after the procedure in all patients is counterintuitive, lacks any evidence base and does not conform to the principles of best practice. In patients with heart failure, although the underlying condition can predispose to lactic acidosis, existing evidence suggests that metformin use is associated with improved outcome rather than increased risk.

Metformin Associated Lactic Acidosis without Organ Dysfunction and Effective Treatment

“…Lactic acidosis, the most severe side effect of metformin therapy, is a very rare complication and it may especially occur in those who have organ dysfunction such as kidney failure, heart failure, lung or liver disease or whose organ dysfunction develops during metformin use [4,5]. The possibility of lactic acidosis is quite low without organ dysfunction.…”

“…Nevertheless, this side effect generally occurs in those who have organ dysfunction (kidney, liver, lung or heart dysfunction etc.) [3,4]. In general, it is not expected in those who have no organ dysfunction.…”

Metformin and heart failure: never say never again

“…The potential mechanisms underlying the beneficial effect of metformin are now receiving attention [27][28][29][30]. Three mechanisms have hitherto been proposed.…”

“…The presence of HF no longer represents a contraindication to metformin use [17,27,29]. Indeed, the US Food and Drug Administration (FDA) has removed HF as an absolute contraindication to metformin use [44,45].…”

“…In conclusion, HF may no longer be considered an absolute contraindication for metformin [17,27,29]; conversely, there is ample evidence to suggest that this agent might reduce the risk of incident HF and mortality in T2DM [11][12][13][14][15][16]18,19] and also improve 1-year survival rates in diabetic patients with HF [14,[21][22][23][24][25][26]. In addition, metformin may exert cardioprotective actions, possibly by AMPK activation and reduced cardiac fibrosis [30][31][32][33][34][35]37].…”