Lactic acidosis during metformin treatment in an elderly diabetic patient with impaired renal function

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.

Fatal metformin overdose: case report and postmortem biochemistry contribution

Metformin is an oral antihyperglycemic agent used in the management of type 2 diabetes mellitus. Lactic acidosis from metformin overdose is a rare complication of metformin therapy and occurs infrequently with therapeutic use. Fatal cases, both accidental and intentional, are extremely rare in clinical practice. Metformin is eliminated by the kidneys, and impaired renal function can result in an increased plasma concentration of the drug. In this report, we describe an autopsy case involving a 70-year-old woman suffering from diabetes mellitus and impaired renal function who received metformin treatment. Metformin concentrations in the peripheral blood collected during hospitalization and femoral blood collected during autopsy were 42 and 47.3 µg/ml, respectively. Lactic acidosis (29.10 mmol/l) was objectified during hospitalization. Furthermore, postmortem biochemistry allowed ketoacidosis to be diagnosed (blood β-hydroxybutyrate, 10,500 µmol/l). Death was attributed to lactic acidosis due to metformin intoxication. Increased plasma concentrations of the drug were attributed to severely impaired renal function. The case emphasizes the usefulness of performing exhaustive toxicology and postmortem biochemistry towards the more complete understanding of the pathophysiological mechanisms that may be involved in the death process.

Metformin and lactic acidosis: cause or coincidence? A review of case reports

OBJECTIVE

Metformin has been associated with the serious side-effect lactic acidosis. However, it remains unclear whether the use of metformin was a cause or a coincidence in lactic acidosis.

DESIGN

A literature search of the Index Medicus (1959-66) and of the databases Embase, Medline, Medline Express (1966-99) was performed using the keywords metformin, biguanides and lactic acidosis. All articles of cases with metformin-induced lactic acidosis (MILA) were cross-referenced.

SUBJECTS

Cases were included for analysis if they met the following criteria: serum pH < or =7.35, lactate concentration > or =5 mmol L(-1).

INTERVENTION

A forum of six experts in intensive care medicine independently categorized the cases in MILA unlikely (score 0), possible MILA (score 1) or probable MILA (score 2).

MAIN OUTCOME MEASURES

Statistical analysis included the paired interobserver agreement (kappa) and multivariate regression analysis.

RESULTS

Of 80 reported cases, 33 were excluded because of insufficient quality. The forum scores of the remaining 47 cases were distributed normally with a mean score of 7 (range 2-10). The kappa-value was 0.041 (SD = 0.24, range -0.514, 0.427). Neither lactate concentration nor mortality correlated with serum metformin concentrations.

CONCLUSIONS

Given the low interobserver agreement and the lack of any relationship between metformin levels and outcome parameters, the concept that there is a simple, causal relationship between metformin use and lactic acidosis in diabetic patients has to be reconsidered.

Comparison of tolbutamide and metformin in elderly diabetic patients

In a randomized double-blind cross-over study the efficacy, metabolic effects, and acceptability of metformin were compared with tolbutamide in 20 diabetic patients aged between 65 and 95 years. No significant differences were noted after treatment in blood glucose control (fasting plasma glucose, metformin 9.1 +/- 2.8 mmol l-1, tolbutamide 8.3 +/- 2.8 mmol l-1; mean change, metformin +1.1 mmol l-1, tolbutamide +0.02 mmol l-1, p = 0.215), domiciliary blood glucose control, fasting insulin, lactate, cholesterol or triglyceride levels. There was a significant difference in weight change between the two treatments (on metformin -2.0 kg, from 63.2 +/- 11.8 to 61.2 +/- 12.3; on tolbutamide, +1.6 kg, from 61.4 +/- 11.1 to 63.0 +/- 12.3; p = 0.001). Initial gastro-intestinal side-effects occurred in 30% of patients with metformin. These were transient and responded to temporary reduction in treatment dosage. Metformin could not be distinguished from tolbutamide in elderly diabetic patients, except in that it was associated with weight loss.

Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update

Oral hypoglycaemic drugs, sulphonylureas and biguanides, occupy an important place in the treatment of Type II (non-insulin-dependent) diabetic patients who fail to respond satisfactorily to diet therapy and physical exercise. Although the precise mechanisms of action of these compounds are still poorly understood, there is sufficient agreement that sulphonylureas have both pancreatic and extrapancreatic effects, whereas biguanides have predominantly extrapancreatic actions. By using labelled compounds or measuring the circulating concentrations, the main pharmacokinetic properties of oral hypoglycaemic agents have been assessed and, in some cases, their pharmacokinetic-pharmacodynamic relationships have been evaluated. A correlation between diabetes control and plasma sulphonylurea or biguanide concentrations is generally lacking at the steady-state, with the possible exception of long-acting agents; after either oral or intravenous dosing, the reduction of plasma glucose is usually related to the increased circulating drug concentrations. The toxic effects of oral hypoglycaemic drugs are more frequent in the elderly and in the presence of conditions that may lead to drug accumulation or potentiation (increased dosage, use of long-acting compounds, hepatic and renal disease, interaction with other drugs); however, a relationship between toxic effects and drug plasma levels has been reported only for biguanides.

[Physiopathological approach to pathological hyperlactatemia in the diabetic patient. Value of blood metformin]

Type B lactic acidosis, or pathological hyperlactatemia (PHL), is defined by an arterial lactate level greater than 5 mmol X l-1. It is a known and severe complication of diabetes mellitus treated with biguanide hypoglycaemic agents, particularly phenformin which was taken off the French pharmaceutical market in 1977. Metformin, which remains the only biguanide hypoglycaemic agent currently prescribed in France, may also lead to this complication. However it does so less frequently and mostly in the diabetic presenting with renal failure. A few well studied cases showed that PHL could be correlated with excessive metformin blood levels, i.e. a toxic mechanism. In order to find out whether this toxic mechanism was the real cause of PHL in diabetics treated with metformin, a systematic study of metformin blood levels was carried out in 20 such patients. They had all been admitted to a critical care unit presenting with PHL. The results of this study led us to distinguish between two groups of patients. The seven patients of the first group had high metformin blood levels (4.3 to 65.8 micrograms X l-1). In these, renal excretion or extrarenal dialysis lowered or normalized their hyperlactatemia, and six of the seven recovered from PHL. In the second group, with thirteen patients, metformin blood levels were within the normal therapeutic range (0.225 to 3 micrograms X l-1) for seven patients and close to zero for the other six. This second group received the same treatment as the first one. Only three patients recovered, the others all died.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug and chemical-induced metabolic acidosis

Metabolic acidosis produced by drugs and/or chemicals can be conveniently divided into those with an increase in the anion gap (anion gap = Na- (Cl + HCO3)) and those with a normal anion gap. The increase in the anion gap is due to the accumulation of unmeasured organic anions, such as lactate or acetoacetate and beta-hydroxybutyrate, as occurs in ketoacidosis and lactic acidosis, or the accumulation of toxic anions such as formate or glycolate, as occurs with the ingestion of methanol or ethylene glycol. Increased concentrations of lactic acid may also be present in the toxic forms of metabolic acidosis. The most common drugs and chemicals that induce the anion gap type of acidosis are biguanides, alcohols, polyhydric sugars, salicylates, cyanide and carbon monoxide. In normal anion gap acidosis the reduction in bicarbonate is balanced by a reciprocal increase in the chloride concentration so that the sum of the two remains unchanged. Normal anion gap acidosis is caused by carbonic anhydrase inhibitors, hydrochloride salts of amino acids, toluene, amphotericin, spironolactone and non-steroidal anti-inflammatory drugs. The mechanism by which these substances produce metabolic acidosis and the therapy are discussed.