Metformin and lactic acidosis in patients with type 2 diabetes--from pride and prejudice to sense and sensibility

The Association between Metformin Therapy and Lactic Acidosis

INTRODUCTION AND OBJECTIVES

There is increasing evidence to suggest that therapeutic doses of metformin are unlikely to cause lactic acidosis. The aims of this research were (1) to formally evaluate the association between metformin therapy and lactic acidosis in published case reports using two causality scoring systems, (2) to determine the frequency of pre-existing independent risk factors in published metformin-associated lactic acidosis cases, (3) to investigate the association between risk factors and mortality in metformin-associated lactic acidosis cases, and (4) to explore the relationship between prescribed metformin doses, elevated metformin plasma concentrations and the development of lactic acidosis in cases with chronic renal impairment.

METHODS

A systematic review was conducted to identify metformin-associated lactic acidosis cases. Causality was assessed using the World Health Organisation-Uppsala Monitoring Centre system and the Naranjo adverse drug reaction probability scale. Compliance to dosing guidelines was investigated for cases with chronic renal impairment as well as the association between steady-state plasma metformin concentrations prior to admission.

RESULTS

We identified 559 metformin-associated lactic acidosis cases. Almost all cases reviewed (97%) presented with independent risk factors for lactic acidosis. The prescribed metformin dose exceeded published guidelines in 60% of cases in patients with impaired kidney function. Metformin steady-state plasma concentrations prior to admission were predicted to be below the proposed upper limit of the therapeutic range of 5 mg/L.

CONCLUSIONS

Almost all cases of metformin-associated lactic acidosis reviewed presented with independent risk factors for lactic acidosis, supporting the suggestion that metformin plays a contributory role. The prescribed metformin dose, on average, exceeded the dosing recommendations by 1000 mg/day in patients with varying degrees of renal impairment but the predicted pre-admission plasma concentrations did not exceed the therapeutic range.

Monitoring metformin in cardiac patients exposed to contrast media using ultra-high-performance liquid chromatography tandem mass-spectrometry

BACKGROUND

There is no evidence that the use of contrast media (CM) in diabetic patients with serum creatinine <130 μmole/L leads to metformin accumulation and subsequent lactic acidosis. Therefore, the objective of this investigation was to monitor cardiac patients for the effects of CM on their metformin plasma concentration and serum creatinine clearance (ClCr).

METHODS

Metformin plasma concentrations were measured by a new, fully validated specific, precise, and accurate ultra-high-performance liquid chromatography tandem mass-spectrometric assay. The detection was performed using positive electrospray ionization in the multiple reaction monitoring mode. Fifty patients with serum creatinine levels <130 μmole/L were monitored for the effect of CM exposure on metformin concentration and ClCr. Pharmacokinetic parameters were calculated in 8 of these patients, and metformin accumulation was monitored in 10 patients before and after their exposure to CM.

RESULTS

Linear response (r ≥ 0.998) was observed over the range of 5-2000 ng/mL of metformin, with the lower limit of quantification of 2.3 ng/mL. The intraday and interday precision (relative standard deviation) values were <13%, and the accuracy (relative error) was <-10% for metformin concentrations. The assay was sensitive to follow the pharmacokinetics of metformin in humans during a dosing interval after an oral dose at steady state. Metformin pharmacokinetic parameters were estimated in 8 patients exposed to CM. The mean C(max) of 1.9 ± 0.6 mg/L was attained at 4.1 ± 1.9 hours. There was no evidence of any drug accumulation or altered elimination due to the exposure to CM in the current population. ClCr showed no significant difference (P > 0.05) before (92.8 ± 11.3 mL/min) and after 48 hours (90.5 ± 10.5 mL/min) of exposure to CM.

CONCLUSIONS

Our data suggest that the recommendation to withhold metformin in diabetic patients during CM exposure could be revised to withholding the drug only in patients with moderate to severe renal dysfunction.

Metformin and heart failure: never say never again

Metformin represents the cornerstone of treatment for type 2 diabetes mellitus. Traditionally, heart failure (HF) was considered a contraindication to its use. However, more recent evidence has shown that this should no longer be the case. Indeed, studies have demonstrated that metformin may even reduce the risk of incident HF and mortality in diabetic patients, while improving up to 2-year survival rates in those with HF. In addition, it appears to exert cardioprotective actions. Although longer follow-up data and more explicit information about the situation in patients with very advanced HF are needed, the cardiac safety of metformin has profound clinical implications and may be anticipated to further encourage its widespread use.

Metformin: diamonds are forever

Metformin has now been established as the drug of choice for the first-line management of type 2 diabetes mellitus. It reduces insulin resistance, improves glycaemic control, and can be safely combined with other classes of oral hypoglycaemic agents. Equally important, metformin has been shown to have a significant beneficial effect on cardiovascular morbidity. Moreover, this agent acts favourably on blood pressure, lipids, haemostasis and other features of the metabolic syndrome. Metformin also contributes to weight reduction and diabetes prevention.