Although metformin has been used for over 60 years, the balance between the drug's beneficial and adverse effects is still subject to debate. Following an analysis of how cases of so-called "metformin-associated lactic acidosis" (MALA) are reported in the literature, the present article reviews the pitfalls to be avoided when assessing the purported association between metformin and lactic acidosis. By starting from pathophysiological considerations, we propose a new paradigm for lactic acidosis in metformin-treated patients. Metformin therapy does not necessarily induce metformin accumulation, just as metformin accumulation does not necessarily induce hyperlactatemia, and hyperlactatemia does not necessarily induce lactic acidosis. In contrast to the conventional view, MALA probably accounts for a smaller proportion of cases than either metformin-unrelated lactic acidosis or metformin-induced lactic acidosis. Lastly, this review highlights the need for substantial improvements in the reporting of cases of lactic acidosis in metformin-treated patients. Accordingly, we propose a check-list as a guide to clinical practice.

Provided that the dose is adjusted for renal function, metformin treatment appears to be safe and still pharmacologically efficacious in moderate-to-severe CKD.

Although metformin has been available for over 50 years and it is the key medication in first-line treatment of type 2 diabetes mellitus, major methodological and/or conceptual errors have confounded the literature on its therapeutic concentrations.

AimsAnalysis of the prognostic values of blood pH and lactate and plasma metformin concentrations in severe metformin-associated lactic acidosis may help to resolve the following paradox: metformin provides impressive, beneficial effects but is also associated with life-threatening adverse effects.Research design and methodsOn the basis of 869 pharmacovigilance reports on MALA with available data on arterial pH and lactate concentration, plasma metformin concentration and outcome, we selected cases with a pH < 7.0 and a lactate concentration >10 mmol/L. Outcomes were compared with those described for severe metformin-independent lactic acidosis.ResultsFifty-six patients met the above-mentioned criteria. The mean arterial pH and lactate values were 6.75 ± 0.17 and 23.07 ± 6.94 mmol/L, respectively. The survival rate was 53%, even with pH values as low as 6.5 and lactate and metformin concentrations as high as 35.3 mmol/L and 160 mg/L (normal < 1 mg/L), respectively. Survivors and non-survivors did not differ significantly in terms of the mean arterial pH and lactate concentration. The mean metformin concentration was higher in patients who subsequently died but this difference was due to a very high value (188 mg/L) in one patient in this group, in whom several triggering factors were combined. Sepsis, multidrug overdoses and the presence of at least two triggering factors for lactic acidosis were observed significantly more frequently in non-survivors (p = 0.007, 0.04, and 0.005, respectively). This contrasts with a study of metformin-independent lactic acidosis in which there were no survivors, despite less severe acidosis on average (mean pH: 6.86).ConclusionsIn 56 cases of severe metformin-associated lactic acidosis, blood pH and lactate did not have prognostic value. One can reasonably rule out the extent of metformin accumulation as a prognostic factor. Ultimately, the determinants of metformin-associated lactic acidosis appear to be the nature and number of triggering factors. Strikingly, most patients survived - despite a mean pH that is incompatible with a favorable outcome under other circumstances.

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The overall mortality rate for MALA was around 50% during the period 1960-2000 but has since fallen to around 25%.

Background/Aims: It has become clear that metformin exerts pleiotropic actions beyond its glucose-lowering agent effect. In this review, we summarise the state of the art concerning the potential renoprotective effects of metformin in vitro, animal models and clinical nephrology. Methods: A literature search was performed in PUBMED, ScienceDirect, between January 1957 and March 2017 using the following keywords: “metformin,” “nephroprotection,” “renoprotection,” “survival,” “renal failure,” “chronic kidney diseases,” “fibrosis,” “polycystic kidney disease” and “microalbuminuria.” Results: A recent review of 17 observational studies concluded that metformin use appeared associated with reduced all-cause mortality in patients with CKD. Metformin has been shown to exert positive effects on the kidney in vitro and animal models representing different types of renal diseases, from acute kidney injury to chronic kidney disease. A retrospective cohort study from the Scientific Registry of Transplant Recipients indicated that metformin was associated with lower adjusted hazards for living donor and deceased donor allograft survival at 3 years posttransplant, and with lower mortality. Conclusion: Based on experimental evidence and some relevant clinical observations, metformin seems to be a promising drug in the treatment of progressive renal damage. RCT studies are the next essential step.

In general, proposals for continuing or stopping metformin therapy in CKD involve a threshold (whether based on serum creatinine or estimated glomerular filtration rate) rather than the dose adjustment as a function of renal status (in stable patients) performed for other drugs excreted by the kidney.