A Pharmacokinetic Analysis of Hemodialysis for Metformin-Associated Lactic Acidosis

Metformin-associated lactic acidosis (MALA): Is it an underestimated entity? A retrospective, single-center case series

INTRODUCTION

Metformin is widely considered a first-line antiglycemic agent due to its cost-effectiveness and favorable adverse effect profile. However, its use is prohibited in patients with an estimated glomerular filtration rate <30 mL/min/1.73 m2 , due to the risk of potentially lethal metformin-associated lactic acidosis (MALA). We sought to evaluate MALA cases and outcomes at our institution.

METHODS

In this observational, retrospective case series, we reviewed our EMR for all patients who had a metformin level drawn between January 2013 and May 2022 to identify individuals who met the diagnostic criteria for MALA. We evaluated risk factors for MALA, the relationship between metformin level, blood pH, serum bicarbonate, and lactate level and clinical outcomes of ventilator dependency, renal replacement therapy requirement, renal recovery in acute kidney injury (AKI) patients, and survival.

FINDINGS

A total of 107 patients had metformin levels drawn, of which 19 patients met the diagnostic criteria for MALA. In our case series, MALA was primarily seen in AKI (15 patients) secondary to dehydration and sepsis, followed by end-stage renal disease (ESRD) (4 patients). Intubation was required in 17 patients, of whom 8 were successfully extubated after a mean duration of 14 days. Sixteen patients received renal replacement therapy (RRT). Intermittent hemodialysis (IHD) was performed in nine, continuous renal replacement therapy (CRRT) in four, and sequential therapy of IHD and CRRT in three patients. Seven patients, all in the AKI group (46.7%), died while all ESRD patients survived, accounting for an overall mortality rate of 36.8%. Among the eight surviving AKI patients, four had complete renal recovery with renal function returning to baseline, three had partial renal recovery, and one continued to require IHD at the time of discharge to a rehabilitation facility.

DISCUSSION

MALA may be an underrecognized entity. A high level of clinical suspicion leading to prompt and aggressive treatment with RRT may improve mortality rates. Provider and patient education is of paramount importance for safe use of metformin.

Calcium-Citrate Anticoagulation during Continuous Renal Replacement Therapy in Patients with Metformin Intoxication: A Case Series, Mathematical Estimation of Citrate Accumulation, and Literature Review

INTRODUCTION

Metformin intoxication causes lactic acidosis by inhibiting Krebs' cycle and oxidative phosphorylation. Continuous renal replacement therapy (CRRT) is recommended for metformin removal in critically ill patients. According to current guidelines, regional citrate anticoagulation (RCA) is the first-line strategy. However, since metformin also inhibits citrate metabolism, a risk of citrate accumulation could be hypothesized. In the present study, we monitored the potential citrate accumulation in metformin-associated lactic acidosis (MALA) patients treated with CRRT and RCA using the physical-chemical approach to acid-base interpretation.

METHODS

We collected a case series of 3 patients with MALA. Patients were treated with continuous venovenous hemofiltration (CVVH), and RCA was performed with diluted citrate solution. Citrate accumulation was monitored through two methods: the ratio between total and ionized plasma calcium concentrations (T/I calcium ratio) above 2.5 and the strong ion gap (SIG) to identify an increased concentration of unmeasured anions. Lastly, a mathematical model was developed to estimate the expected citrate accumulation during CVVH and RCA.

RESULTS

All 3 patients showed a resolution of MALA after the treatment with CVVH. The T/I calcium ratio was consistently below 2.5, and SIG decreased, reaching values lower than 6 mEq/L after 48 h of CVVH treatment. According to the mathematical model, the estimated SIG without citrate metabolism should have been around 21 mEq/L due to citrate accumulation.

CONCLUSIONS

In our clinical management, no signs of citrate accumulation were recorded in MALA patients during treatment with CVVH and RCA. Our data support the safe use of diluted citrate to perform RCA during metformin intoxication.

Metformin, chronic nephropathy and lactic acidosis: a multi-faceted issue for the nephrologist

Metformin is currently considered a first-line therapy in type 2 diabetic patients. After issuing warnings for decades about the risks of lactic acidosis in patients with chronic nephropathy, metformin is now being re-evaluated. The most recent evidence from the literature has demonstrated both a low, acceptable risk of lactic acidosis and a series of favorable effects, which go beyond its hypoglycemic activity. Patients treated with metformin show a significant mortality reduction and lower progression towards end-stage renal disease in comparison with those treated with other hypoglycemic drugs. Concerning lactic acidosis, in the last few years it has been shown how lactic acidosis almost always developed when patients kept taking the drug in the face of a concomitant disease or situation such as sepsis, fever, diarrhea, vomiting, which reduced metformin renal clearance. Actually, clearance of metformin is mainly renal, both by glomerular filtration and tubular secretion (apparent clearance 933–1317 ml/min, half-life < 3 h). As regards treatment, in cases of lactic acidosis complicated by acute kidney injury, continuous renal replacement therapy (CRRT) plays a crucial role. Besides the elimination of metformin, CRRT  improves survival by correcting acidosis, electrolyte alterations, and maintaining fluid balance. Lactic acidosis almost always develops because of preventable drug accumulation. Therefore, prevention is a key factor. Patients should be aware that discontinuation for a limited time does not affect their health, even when it may be inappropriate, but it may avoid a serious, potentially fatal adverse event.