Metformin-Associated Lactic Acidosis Precipitated by Diarrhea

Optimizing metformin therapy in practice: Tailoring therapy in specific patient groups to improve tolerability, efficacy and outcomes

Metformin is the first-line medication for type 2 diabetes. It is effective and safe, provided some caution is taken in specific populations. In patients with chronic kidney disease, metformin may provide long-term benefits, and it is a first-line therapy for diabetes, but the estimated glomerular filtration rate (eGFR) must be assessed regularly, to minimize the risk for metformin accumulation. When eGFR is 30-60 mL/min/1.73m2, the dose should be reconsidered, and sick-days education provided. Metformin should be discontinued when eGFR falls below 30 mL/min/1.73m2. Metformin accumulation may increase the risk for lactic acidosis if concomitant risk factors for hyperlactataemia (liver or respiratory insufficiency, sepsis, acute heart failure) are present; in these conditions, metformin is contraindicated, even although the available evidence is reassuring. Patients on metformin often complain of gastrointestinal side effects (mainly diarrhoea and nausea) during therapy initiation, but they may sometimes occur after years of stable therapy. These usually resolve if the dose is carefully titrated, or by switching to the extended-release formulation. Patients with obesity may benefit from the significant, although modest, metformin-associated weight loss and appetite reduction. During pregnancy, metformin is associated with a reduction of pregnancy complications, especially in obese women, but some concern remains, because metformin crosses the placenta, and it is associated with a significantly lower mean birth weight than insulin. In the elderly, gastrointestinal tolerability and renal function must be reassessed more often. Vitamin B-12 should be screened regularly in long-time metformin users because metformin may induce clinical vitamin B-12 deficiency.

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.

Drug-Induced Metabolic Acidosis

Metabolic acidosis could emerge from diseases disrupting acid-base equilibrium or from drugs that induce similar derangements. Occurrences are usually accompanied by comorbid conditions of drug-induced metabolic acidosis, and clinical outcomes may range from mild to fatal. It is imperative that clinicians not only are fully aware of the list of drugs that may lead to metabolic acidosis but also understand the underlying pathogenic mechanisms. In this review, we categorized drug-induced metabolic acidosis in terms of pathophysiological mechanisms, as well as individual drugs’ characteristics.

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.

Pharmacologically-induced metabolic acidosis: a review

Metabolic acidosis may occasionally develop in the course of treatment with drugs used in everyday clinical practice, as well as with the exposure to certain chemicals. Drug-induced metabolic acidosis, although usually mild, may well be life-threatening, as in cases of lactic acidosis complicating antiretroviral therapy or treatment with biguanides. Therefore, a detailed medical history, with special attention to the recent use of culprit medications, is essential in patients with acid-base derangements. Effective clinical management can be handled through awareness of the adverse effect of certain pharmaceutical compounds on the acid-base status. In this review, we evaluate relevant literature with regard to metabolic acidosis associated with specific drug treatment, and discuss the clinical setting and underlying pathophysiological mechanisms. These mechanisms involve renal inability to excrete the dietary H+ load (including types I and IV renal tubular acidoses), metabolic acidosis owing to increased H+ load (including lactic acidosis, ketoacidosis, ingestion of various substances, administration of hyperalimentation solutions and massive rhabdomyolysis) and metabolic acidosis due to HCO3- loss (including gastrointestinal loss and type II renal tubular acidosis). Determinations of arterial blood gases, the serum anion gap and, in some circumstances, the serum osmolar gap are helpful in delineating the pathogenesis of the acid-base disorder. In all cases of drug-related metabolic acidosis, discontinuation of the culprit medications and avoidance of readministration is advised.

The MALAdy of metformin poisoning: Is CVVH the cure?

Inadvertent or intentional metformin overdose can result in death from refractory lactic acidosis. We report a death from metformin-induced refractory lactic acidosis despite aggressive care. A 49-year-old hypertensive diabetic female presented 1 hour after ingesting 60 tablets of 500 mg metformin and 20 combination tablets of 12.5 mg hydrochlorothiazide/20 mg lisinopril. She was awake and alert, with a blood glucose of 579 mg/dL. Chemistry panel revealed lactic acidosis and acute renal failure (arterial blood gas pH, 7.18; pCO(2), 15 mm Hg; pO(2), 127 mm Hg; HCO(3), 6 mmol/L; lactate, 9.6 mmol/L; and creatinine, 1.2 mg/dL [0.8 mg/dL previously]). She received normal saline, sodium bicarbonate, and insulin. On arrival to the intensive care unit she was obtunded, with a blood pressure of 40/25 mm Hg and had worsening acidosis and poor oxygenation (arterial blood gas pH, 6.79; pCO(2), 55; pO(2), 57; HCO(3), 8.4; and base excess of -25 on 100% fractional inspired oxygen). She was intubated and received additional fluid boluses, bicarbonate, and norepinephrine. Continuous veno-venous hemofiltration (CVVH) was started 6 hours after her ingestion. Metformin was 380 microg/mL on CVVH initiation. The patient developed pulseless electrical activity 30 hours after her ingestion, which recurred 20 minutes later. The family requested no further resuscitation. She died 31.5 hours after her ingestion. Metformin concentrations decreased to 97 microg/mL 28 hours after the ingestion on CVVH, with a first-order elimination half-life of 11.3 hours (r(2) = 0.99) and a clearance of 56.2 mL/min. Further investigations on the place of CVVH in the management of the poisoned patient with MALA unable to hemodynamically tolerate conventional hemodialysis may be needed.

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

AIM

To present the cases of lactic acidosis encountered in our department among metformin-treated type 2 diabetic patients and to investigate the role of contraindications to metformin use.

METHODS

A survey of medical records of metformin-treated type 2 diabetic patients hospitalised for various medical conditions during the years 2004-2005 who exhibited elevated serum concentrations of lactic acid.

RESULTS

Seven metformin-treated type 2 diabetic patients were identified who were not attending our department and were hospitalised with elevated serum lactic acid levels (6 developed lactic acidosis). All patients had one or more contraindications to metformin use. Outcome was favourable in 6 patients, while 1 patient with hepatocellular carcinoma died of liver failure.

CONCLUSIONS

So far, metformin is one of the safest first-line oral hypoglycaemic agents. However, caution is needed to avoid patients with evident contraindications. This highlights the need for the practitioner to possess sound clinical judgement when prescribing metformin.