Metformin-associated lactic acidosis

Refractory vasodilatory shock secondary to metformin overdose supported with VA ECMO

•

Metformin overdose can lead to vasodilatory shock refractory to medical management.

•

Extracorporeal circulatory support with venoarterial ECMO is an effective way to manage profound shock associated with metformin overdose.

•

We report the highest recorded serum metformin level in the literature to date.

Metformin overdose may result in vasodilatory shock, lactic acidosis and death. Hemodialysis is an effective means of extracorporeal elimination, but may be insufficient in the shock setting. We present a case of a 39 yo male who presented with hypotension, coma, hypoglycemia, and lactate of 6.5 mmol/L after ingesting an unknown medication. Metformin overdose was suspected, and he was started on hemodialysis. He developed profound vasoplegia refractory to high doses of norepinephrine, vasopressin, epinephrine and phenylephrine. Venoarterial extracorporeal membrane oxygenation (VA ECMO) was initiated and he had full recovery. Serum analysis with high resolution liquid chromatography mass spectrometry revealed a metformin level of 678 μg/mL and trazodone level of 2.1 μg/mL. This case is one of only a handful of reported cases of metformin overdose requiring ECMO support, and we report the highest serum metformin levels in the literature to date. We recommend early aggressive hemodialysis and vasopressor support in all suspected cases of metformin toxicity as well as VA ECMO if refractory to these therapies.

Objective

We present a case of vasodilatory shock secondary to metformin overdose requiring venoarterial extracorporeal membrane oxygenation (VA ECMO) support. This case is one of only a handful of reported cases of metformin overdose requiring ECMO support, and we report the highest serum metformin levels in the literature to date.

Data sources

University of San Francisco, Fresno.

Study design

Case report.

Data extraction

Clinical records and high resolution liquid chromatography mass spectroscopy analysis.

Data synthesis

None.

Conclusions

Venoarterial ECMO provided an effective means of hemodynamic support for a patient with severe metformin toxicity.

The Gut Microbiome, Metformin, and Aging

Metformin has been extensively used for the treatment of type 2 diabetes, and it may also promote healthy aging. Despite its widespread use and versatility, metformin's mechanisms of action remain elusive. The gut typically harbors thousands of bacterial species, and as the concentration of metformin is much higher in the gut as compared to plasma, it is plausible that microbiome-drug-host interactions may influence the functions of metformin. Detrimental perturbations in the aging gut microbiome lead to the activation of the innate immune response concomitant with chronic low-grade inflammation. With the effectiveness of metformin in diabetes and antiaging varying among individuals, there is reason to believe that the gut microbiome plays a role in the efficacy of metformin. Metformin has been implicated in the promotion and maintenance of a healthy gut microbiome and reduces many age-related degenerative pathologies. Mechanistic understanding of metformin in the promotion of a healthy gut microbiome and aging will require a systems-level approach. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

A Rare Case of Metformin Intoxication with Mortal Course

Metformin-associated lactic acidosis is a rare side effect in metformin poisoning. There is conflicting data about mortality rates changing from 3% to 83%. We aimed to discuss a case that developed lactic acidosis and acute renal failure progressing to mortality due to metformin intoxication. A 33 year-old female patient was admitted to the emergency department, with nausea and vomiting after taking 30 tablets of 1000 mg metformin. In the 2nd hour of follow-up, patient was observed to develop lactic acidosis which did not recover despite the infusion replacement treatments and hemodialysis. Following the development of respiratory failure, under mechanical ventilation, the patient developed cardiac arrest at the 48th hour of her admission. In metformin intoxications, it should be remembered that acidosis deepens very quickly and can progress with mortality despite optimal supportive therapy. More specific recommendations and further studies are required for the management and treatment of acute metformin-associated lactic acidosis.

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.

Review of Biguanide (Metformin) Toxicity

In the 1920s, guanidine, the active component of Galega officinalis, was shown to lower glucose levels and used to synthesize several antidiabetic compounds. Metformin (1,1 dimethylbiguanide) is the most well-known and currently the only marketed biguanide in the United States, United Kingdom, Canada, and Australia for the treatment of non-insulin-dependent diabetes mellitus. Although phenformin was removed from the US market in the 1970s, it is still available around the world and can be found in unregulated herbal supplements. Adverse events associated with therapeutic use of biguanides include gastrointestinal upset, vitamin B₁₂ deficiency, and hemolytic anemia. Although the incidence is low, metformin toxicity can lead to hyperlactatemia and metabolic acidosis. Since metformin is predominantly eliminated from the body by the kidneys, toxicity can occur when metformin accumulates due to poor clearance from renal insufficiency or in the overdose setting. The dominant source of metabolic acidosis associated with hyperlactatemia in metformin toxicity is the rapid cytosolic adenosine triphosphate (ATP) turnover when complex I is inhibited and oxidative phosphorylation cannot adequately recycle the vast quantity of H+ from ATP hydrolysis. Although metabolic acidosis and hyperlactatemia are markers of metformin toxicity, the degree of hyperlactatemia and severity of acidemia have not been shown to be of prognostic value. Regardless of the etiology of toxicity, treatment should include supportive care and consideration for adjunct therapies such as gastrointestinal decontamination, glucose and insulin, alkalinization, extracorporeal techniques to reduce metformin body burden, and metabolic rescue.

Hypoglycemia and severe lactic acidosis in a dog following metformin exposure

Hypoglycemia and lactic acidosis are rare complications with metformin use in humans. As metformin is not commonly used in veterinary medicine, severe adverse effects secondary to exposure are not known. Awareness of potentially life-threatening complications with metformin exposure is an important addition to the veterinary literature.

Extracorporeal Treatment for Metformin Poisoning: Systematic Review and Recommendations From the Extracorporeal Treatments in Poisoning Workgroup

BACKGROUND

Metformin toxicity, a challenging clinical entity, is associated with a mortality of 30%. The role of extracorporeal treatments such as hemodialysis is poorly defined at present. Here, the Extracorporeal Treatments In Poisoning workgroup, comprising international experts representing diverse professions, presents its systematic review and clinical recommendations for extracorporeal treatment in metformin poisoning.

METHODS

A systematic literature search was performed, data extracted, findings summarized, and structured voting statements developed. A two-round modified Delphi method was used to achieve consensus on voting statements and RAND/UCLA Appropriateness Method to quantify disagreement. Anonymized votes and opinions were compiled and discussed. A second vote determined the final recommendations.

RESULTS

One hundred seventy-five articles were identified, including 63 deaths: one observational study, 160 case reports or series, 11 studies of descriptive cohorts, and three pharmacokinetic studies in end-stage renal disease, yielding a very low quality of evidence for all recommendations. The workgroup concluded that metformin is moderately dialyzable (level of evidence C) and made the following recommendations: extracorporeal treatment is recommended in severe metformin poisoning (1D). Indications for extracorporeal treatment include lactate concentration greater than 20 mmol/L (1D), pH less than or equal to 7.0 (1D), shock (1D), failure of standard supportive measures (1D), and decreased level of consciousness (2D). Extracorporeal treatment should be continued until the lactate concentration is less than 3 mmol/L (1D) and pH greater than 7.35 (1D), at which time close monitoring is warranted to determine the need for additional courses of extracorporeal treatment. Intermittent hemodialysis is preferred initially (1D), but continuous renal replacement therapies may be considered if hemodialysis is unavailable (2D). Repeat extracorporeal treatment sessions may use hemodialysis (1D) or continuous renal replacement therapy (1D).

CONCLUSION

Metformin poisoning with lactic acidosis appears to be amenable to extracorporeal treatments. Despite clinical evidence comprised mostly of case reports and suboptimal toxicokinetic data, the workgroup recommended extracorporeal removal in the case of severe metformin poisoning.

The interpretation of perioperative lactate abnormalities in patients undergoing cardiac surgery

Hyperlactataemia and lactic acidosis are commonly encountered during and after cardiac surgery. Perioperative lactate production increases in the myocardium, skeletal muscle, lungs and in the splanchnic circulation during cardiopulmonary bypass. Hyperlactataemia has a bimodal distribution in the perioperative period. An early increase in lactate levels, arising intraoperatively or soon after intensive care unit admission, is a familiar and concerning finding for most clinicians. It is highly suggestive of tissue ischaemia and is associated with a prolonged intensive care unit stay, a prolonged requirement for respiratory and cardiovascular support and increased postoperative mortality. Its presence should prompt a thorough search for potential causes of tissue hypoxia. In contrast, late-onset hyperlactataemia, a less well recognised complication, occurs 4 to 24 hours after completion of surgery and is typically associated with preserved cardiac output and oxygen delivery. Risk factors for late-onset hyperlactataemia include hyperglycaemia, long cardiopulmonary bypass time and elevated endogenous catecholamines. Although patients with this complication may have a longer duration of ventilation and intensive care unit length of stay than those with normolactataemia, an association with increased mortality has not been demonstrated. The discovery of late-onset hyperlactataemia should not delay the postoperative progress of an otherwise stable patient following cardiac surgery.

Use of physiologically based pharmacokinetic modeling for assessment of drug-drug interactions

Interactions between co-administered medicines can reduce efficacy or lead to adverse effects. Understanding and managing such interactions is essential in bringing safe and effective medicines to the market. Ideally, interaction potential should be recognized early and minimized in compounds that reach late stages of drug development. Physiologically based pharmacokinetic models combine knowledge of physiological factors with compound-specific properties to simulate how a drug behaves in the human body. These software tools are increasingly used during drug discovery and development and, when integrating relevant in vitro data, can simulate drug interaction potential. This article provides some background and presents illustrative examples. Physiologically based models are an integral tool in the discovery and development of drugs, and can significantly aid our understanding and prediction of drug interactions.

Interactions between tumor cells and microenvironment in breast cancer: a new opportunity for targeted therapy

Breast cancer remains the leading cause of morbidity and second-leading cause of death in women. Despite efforts to uncover new targeted therapies, a vast number of women die due to refractory or recurrent breast tumors. Most breast cancer studies have focused on the intrinsic characteristics of breast tumor cells, including altered growth, proliferation, and metabolism. However, emerging research suggests that the tumor microenvironment can substantially affect relapse rates and therapeutic responses. In this review, we discuss the interactions between the tumor and microenvironment in breast cancer, with regard to mutational profiles and altered metabolism that could serve as potential therapeutic targets. We also describe current technologies available to study these interactions.

Transporter-mediated drug-drug interactions with oral antidiabetic drugs

Uptake transporters (e.g., members of the SLC superfamily of solute carriers) and export proteins (e.g., members of the ABC transporter superfamily) are important determinants for the pharmacokinetics of drugs. Alterations of drug transport due to concomitantly administered drugs that interfere with drug transport may alter the kinetics of drug substrates. In vitro and in vivo studies indicate that many drugs used for the treatment of metabolic disorders and cardiovascular diseases (e.g., oral antidiabetic drugs, statins) are substrates for uptake transporters and export proteins expressed in the intestine, the liver and the kidney. Since most patients with type 2 diabetes receive more than one drug, transporter-mediated drug-drug interactions are important molecular mechanisms leading to alterations in oral antidiabetic drug pharmacokinetics with the risk of adverse drug reactions. This review focuses on uptake transporters of the SLCO/SLC21 (OATP) and SLC22 (OCT/OAT) family of solute carriers and export pumps of the ABC (ATP-binding cassette) transporter superfamily (especially P-glycoprotein) as well as the export proteins of the SLC47 (MATE) family and their role for transporter-mediated drug-drug interactions with oral antidiabetic drugs.

Management of metformin-associated lactic acidosis by continuous renal replacement therapy

BACKGROUND

Metformin-associated lactic acidosis (MALA) is a severe metabolic failure with high related mortality. Although its use is controversial, intermittent hemodialysis is reported to be the most frequently used treatment in conjunction with nonspecific supportive measures. Our aim was to report the evolution and outcome of cases managed by continuous renal replacement therapy (CRRT).

METHODOLOGY AND PRINCIPAL FINDINGS

Over a 3-year period, we retrospectively identified patients admitted to the intensive care unit for severe lactic acidosis caused by metformin. We included patients in our study who were treated with CRRT because of shock. We describe their clinical and biological features at admission and during renal support, as well as their evolution. We enrolled six patients with severe lactic acidosis; the mean pH and mean lactate was 6.92±0.20 and 14.4±5.1 mmol/l, respectively. Patients had high illness severity scores, including the Simplified Acute Physiology Score II (SAPS II) (average score 63±12 points). Early CRRT comprised either venovenous hemofiltration (n = 3) or hemodiafiltration (n = 3) with a mean effluent flow rate of 34±6 ml/kg/h. Metabolic acidosis control and metformin elimination was rapid and there was no rebound. Outcome was favorable in all cases.

CONCLUSIONS AND SIGNIFICANCE

Standard use of CRRT efficiently treated MALA in association with symptomatic organ supportive therapies.

Metformin overdose with a resultant serum pH of 6.59: survival without sequalae

Metformin, widely used in the treatment of diabetes mellitus, is known to cause lactic acidosis in both therapeutic use and after an overdose. We report the case of a 40-year-old woman who claimed to have ingested between 75 and 100 grams of metformin and subsequently developed severe lactic acidosis. She eventually developed a peak serum lactate level of 40.0 mmol/L and a serum pH nadir of 6.59 and became obtunded, hypotensive, and hypothermic. After aggressive supportive therapy with mechanical ventilation, vasopressor agents, sodium bicarbonate, and hemodialysis, her metabolic derangements steadily improved and she made a complete recovery without any residual sequelae. Her admission serum metformin concentration was later determined to be 160 microg/mL (therapeutic range is 1-2 microg/mL). There are several case reports and case series describing lactic acidosis secondary to metformin ingestion, although the exact mechanism remains unclear. The overall management of metformin overdose is reviewed. This case represents the largest reported amount of ingested metformin, the lowest serum pH, and the highest serum lactate concentration in any intentional metformin overdose survivor in the literature. Despite potentially lethal metabolic derangements, such patients can survive with aggressive supportive care.

Extracorporeal Removal Techniques for the Poisoned Patient: A Review for the Intensivist

The kidney is able to rapidly eliminate many water-soluble xenobiotics (exogenous chemicals). However, in the face of extraordinary serum concentrations of these xenobiotics or renal dysfunction, alternative elimination techniques often become necessary. Extracorporeal removal (ECR) techniques are used to increase the clearance of xenobiotics. These techniques include hemodialysis (HD), charcoal hemoperfusion (HP), and modalities grouped under the heading of continuous renal replacement therapy (CRRT): continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodiafiltration (CVVHDF). Extracorporeal removal is limited to patients with significant or potentially significant clinical poisoning because the resources required to perform ECR are great. Therefore, most patients who are treated with these techniques are being cared for in intensive care units (ICUs). Our goal in this review is to discuss the properties that make xenobiotics amenable to removal by ECR and the advantages and disadvantages of the individual techniques. We discuss xenobiotics that constitute clear indications for ECR, including the toxic alcohols, salicylates, and lithium. We review the use of CRRT, a modality for which clear indications for treatment of poisonings are currently lacking.

Treatment of lactic acidosis: appropriate confusion

BACKGROUND

Lactic acidosis (LA) is common in hospitalized patients and is associated with poor clinical outcomes. There have been major recent advances in our understanding of lactate generation and physiology. However, treatment of LA is an area of controversy and uncertainty, and the use of agents to raise pH is not clearly beneficial.

AIM AND METHODS

We reviewed animal and human studies on the pathogenesis, impact, and treatment of LA, published in the English language and available through the PubMed/MEDLINE database. Our aim was to clarify the physiology of the generation of LA, its impact on outcomes, and the different treatment modalities available. We also examined relevant data regarding LA induced by medications commonly prescribed by hospitalists: biguanides, nucleoside analog reverse-transcriptase inhibitors (NRTIs), linezolid, and lorazepam.

RESULTS/CONCLUSIONS

Lactic acid is a marker of tissue ischemia but it also may accumulate without tissue hypoperfusion. In the latter circumstance, lactic acid accumulation may be an adaptive mechanism-a novel possibility quite in contrast to the traditional view of lactic acid as only a marker of tissue ischemia. Studies on the treatment of LA with sodium bicarbonate or other buffers fail to show consistent clinical benefit. Severe acidemia in the setting of LA is a particularly poorly studied area. In the settings of medication-induced LA, optimal treatment, apart from prompt cessation of the offending agent, is still unclear.

Occult metformin toxicity in three patients with profound lactic acidosis

There are 20.8 million Americans with diabetes, and metformin is the most commonly prescribed oral diabetes agent. A review of our metformin experience highlights common pitfalls that lead to life-threatening or fatal poisonings. We describe 3 patients with metformin toxicity; 2 of 3 patients were prescribed metformin despite end-stage renal disease (ESRD). Case 1: a 40-year-old woman presented after a polysubstance overdose. Within 8 h, vomiting and lethargy developed; a profound acidosis, pH 6.95, pCO(2) 26, pO(2) 195, and elevated serum lactate 21 mmol/L (ref 0.5-1.6 mmol/L) were noted. Further inquiry revealed that the patient had ingested metformin. She was intubated; bicarbonate therapy and hemodialysis were initiated; however, she became hypotensive and died. A metformin level was 150 μg/mL (therapeutic 1-2 μg/mL). Case 2: a 69-year-old woman with non-insulin-dependent diabetes mellitus (NIDDM) and ESRD presented to the Emergency Department (ED), having missed dialysis. She was sluggish and complained of abdominal pain; an acidosis, pH 7.37, pCO(2) 20, pO(2) 171; anion gap 38, and elevated serum lactate 18.9 mmol/L were noted. Hemodialysis was initiated when it was revealed that she took metformin daily. She improved rapidly and a metformin level was 27.4 μg/mL. Case 3: a 57-year-old woman with a history of NIDDM and ESRD presented with dyspnea. Laboratory studies showed pH 7.03, pCO(2) 21, pO(2) 99; anion gap 36, and lactate 16 mmol/L. Bicarbonate therapy and hemodialysis were initiated after discovering that she had recently been prescribed metformin. She had a fatal cardiac arrest after dialysis was completed. We describe 3 ED patients with occult metformin toxicity diagnosed after laboratory results showed an anion gap metabolic acidosis and elevated lactate levels. All patients had lethargy, vomiting, or abdominal pain, also suggesting sepsis or mesenteric infarction. Despite sodium bicarbonate therapy and hemodialysis, metformin-associated lactic acidosis was fatal in 2 of 3 patients. Emergency Physicians must be vigilant to recognize metformin toxicity in patients at high risk for metformin-associated lactic acidosis.

Acidose lactique et metformine

OBJECTIVE

The aims of this review are to precise the pathophysiological mechanisms leading to biguanide-associated lactic acidosis, to give elements of diagnosis, and to underline the precautionary conditions for prescribing these drugs by an improvement in physicians and patient's education.

DATA SOURCES

A PubMed database research in English and French language reports published until December 2005. The keywords were: lactic acidosis, metformin, biguanide, diabetes mellitus.

DATA EXTRACTION

Data in selected articles were reviewed, clinical and basic science research relevant informations were extracted.

DATA SYNTHESIS

Metformin, which is an oral antidiabetic agent, is the only one biguanide available in France. It acts by enhancing the sensitivity to insulin by a decrease in the hepatic glucose production and an increase in its peripheral use. In term of glycemic control, it has the same efficiency than the other hypoglycemic agents. It represents the treatment of choice for overweight type 2 diabetic patients because of its beneficial effects on the weight loss and on the cardiovascular complications. The incidence of metformin-associated lactic acidosis is very low when contra-indications and appropriate rules for prescribing this drug are respected. The relationship between metformin and lactic acidosis remains largely controversial. In practical, we can distinguish three situations which have different prognosis. In the first case, metformin seems to be responsible for lactic acidosis because of self-poisoning or accidental overdose, and prognosis is good. In the second case, the association between metformin and lactic acidosis is coincidental rather than causal, and may be induced by an underlying organ failure. In the last case there is a cause of lactic acidosis which is worsened by a precipitating factor leading to metformin accumulation. The 2 latter situations are very severe as mortality rate is about 50%. Symptomatic treatments and renal replacement therapy which allows metformin removal are the curative treatment. Prevention is essential. It requires the respect of metformin contraindications and a better education of physicians and patients for a safe prescription.

CONCLUSION

Due to its beneficial effects, metformin is the gold standard treatment for overweight type 2 diabetic patients. The essential precautionary conditions for prescribing metformin as well as the respect of its contra-indications permit largely to prevent lactic acidosis. This complication is serious when it is associated with intercurrent illnesses and metformin accumulation. The curative treatment is based on renal replacement therapy. Prevention only rests on the respect of the contra-indications. Education of physicians and patients concerning the rules of prescription remains essential.

Dialysis Rounds A Dialysis Case Presentation and Discussion Edited by Roger A. Rodby: Severe Lactic Acidosis Treated with Prolonged Hemodialysis: Recovery After Massive Overdoses of Metformin

We report two cases of severe lactic acidosis due to massive metformin ingestion. The first case was a 37-year-old man who was discovered several hours after ingesting 45 g of metformin. He had severe lactic acidosis (blood pH 6.81, bicarbonate 4 mEq/L, lactate 25.7 mEq/L). Despite intravenous bicarbonate therapy, he decompensated and was placed on a combination of hemodialysis and charcoal hemoperfusion for a continuous time of 25 hours. His hospital course was complicated by acute renal failure requiring a period of intermittent hemodialysis. He has since made a complete recovery. The second case was a 53-year-old man who ingested 50 g of metformin. He also presented with severe lactic acidosis (blood pH 6.85, bicarbonate 3 mEq/L and lactate 28.4 mEq/L) and deteriorated despite intravenous bicarbonate therapy. He was placed on hemodialysis as a continuous therapy for 21 hours. His hospital course was complicated by acute renal failure requiring a period of intermittent hemodialysis. He has subsequently made a complete recovery. Metformin-associated lactic acidosis carries a high mortality rate. Prolonged hemodialysis should be considered as an early treatment option in these cases.

[Metformin-associated lactic acidosis remains a serious complication of metformin therapy]

We report 4 cases of lactic acidosis in diabetic patients usually treated with metformin. For the first 3 patients, the clinical history was similar because lactic acidosis was precipitated by gastro-intestinal disorders whereas all of them were simultaneously treated with several nephrotoxic drugs. These 3 patients presented with acute renal failure on arrival at hospital. Their issue was fatal whereas any obvious cause of overproduction of lactate was found. The fourth case, which was due to a voluntary intoxication, was the only one presenting with a favourable evolution. The metformin plasma and red blood cell levels were performed for 2 of 4 patients and confirmed the overdose. These observations remind that metformin-associated lactic acidosis remains a serious complication, and that medical doctors must respect strictly contra-indications and guidelines for withdrawing metformin.

Involvement of organic cation transporter 1 in the lactic acidosis caused by metformin

Biguanides are a class of drugs widely used as oral antihyperglycemic agents for the treatment of type 2 diabetes mellitus, but they are associated with lactic acidosis, a lethal side effect. We reported previously that biguanides are good substrates of rat organic cation transporter 1 (Oct1; Slc22a1) and, using Oct1(-/-) mice, that mouse Oct1 is responsible for the hepatic uptake of a biguanide, metformin. In the present study, we investigated whether the liver is the key organ for the lactic acidosis. When mice were given metformin, the blood lactate concentration significantly increased in the wild-type mice, whereas only a slight increase was observed in Oct1(-/-) mice. The plasma concentration of metformin exhibited similar time profiles between the wild-type and Oct1(-/-) mice, suggesting that the liver is the key organ responsible for the lactic acidosis. Furthermore, the extent of the increase in blood lactate caused by three different biguanides (metformin, buformin, and phenformin) was compared with the abilities to reduce oxygen consumption in isolated rat hepatocytes. When rats were given each of these biguanides, the lactate concentration increased significantly. This effect was dose-dependent, and the EC(50) values of metformin, buformin, and phenformin were 734, 119, and 4.97 microM, respectively. All of these biguanides reduced the oxygen consumption by isolated rat hepatocytes in a concentration-dependent manner. When the concentration required to reduce the oxygen consumption to 75% of the control value (from 0.40 to 0.29 micromol/min/mg protein) was compared with the EC(50) value obtained in vivo, a clear correlation was observed among the three biguanides, suggesting that oxygen consumption in isolated rat hepatocytes can be used as an index of the incidence of lactic acidosis.

Metformin-associated lactic acidosis after elective cervical spine fusion: a case report

STUDY DESIGN

A case of metformin-associated lactic acidosis after elective spinal surgery is reported.

OBJECTIVE

To inform spinal surgeons of this potentially fatal side effect and make them aware that metformin should be stopped 48 hours before surgery.

SUMMARY OF BACKGROUND DATA

Metformin is a commonly used oral hypoglycemic agent used in the treatment of non-insulin-dependent diabetes mellitus. A rare side effect of metformin is lactic acidosis, which has a 50% mortality rate. Risk factors for metformin-associated lactic acidosis include renal, hepatic, and cardiac failure. Two cases have been reported in postsurgical patients. No cases of this disorder have been reported after orthopedic procedures.

METHODS

A patient who developed metformin-associated lactic acidosis after cervical spinal fusion is presented.

RESULTS

Recognition of the cause and aggressive medical management led to resolution of the lactic acidosis. Subsequent surgery was uneventful when metformin was discontinued more than 48 hours before surgery.

CONCLUSION

Spinal surgeons should be aware of this preventable, potentially fatal side effect and stop metformin 48 hours before surgery.

Determination of metformin in human plasma by high-performance liquid chromatography with spectrophotometric detection

A simple, selective, sensitive and precise high-performance liquid chromatographic plasma assay for the hypoglycemic agent metformin is described. Acidified samples of plasma were deproteinated with acetonitrile, washed with dichloromethane and the resulting supernatant injected. Chromatography was performed at 40 degrees C by pumping a mobile phase of acetonitrile (250 ml) in pH 7, 0.03 M diammonium hydrogen phosphate buffer (750 ml) at a flow-rate of 1 ml/min through a silica column. Metformin and the internal standard (atenolol) were detected at 240 nm and were eluted 7.8 and 6.8 min, respectively, after injection. No endogenous substances were found to interfere. Calibration curves were linear (r>0.999) from 10 to 2000 ng/ml. The absolute recovery of both metformin and atenolol was greater than 76%. The detection limit and limit of quantitation were 2.5 and 10 ng/ml, respectively. The intra- and inter-day precision (C.V.) was 12%, or less, and the accuracy was within 6.2% of the nominal concentration. This method is suitable for clinical investigation and monitoring metformin concentration.