Do risk factors for lactic acidosis influence dosing of metformin?

Metformin in patients with type 2 diabetes and kidney disease: a systematic review

IMPORTANCE

Metformin is widely viewed as the best initial pharmacological option to lower glucose concentrations in patients with type 2 diabetes mellitus. However, the drug is contraindicated in many individuals with impaired kidney function because of concerns of lactic acidosis.

OBJECTIVE

To assess the risk of lactic acidosis associated with metformin use in individuals with impaired kidney function.

EVIDENCE ACQUISITION

In July 2014, we searched the MEDLINE and Cochrane databases for English-language articles pertaining to metformin, kidney disease, and lactic acidosis in humans between 1950 and June 2014. We excluded reviews, letters, editorials, case reports, small case series, and manuscripts that did not directly pertain to the topic area or that met other exclusion criteria. Of an original 818 articles, 65 were included in this review, including pharmacokinetic/metabolic studies, large case series, retrospective studies, meta-analyses, and a clinical trial.

RESULTS

Although metformin is renally cleared, drug levels generally remain within the therapeutic range and lactate concentrations are not substantially increased when used in patients with mild to moderate chronic kidney disease (estimated glomerular filtration rates, 30-60 mL/min per 1.73 m2). The overall incidence of lactic acidosis in metformin users varies across studies from approximately 3 per 100,000 person-years to 10 per 100,000 person-years and is generally indistinguishable from the background rate in the overall population with diabetes. Data suggesting an increased risk of lactic acidosis in metformin-treated patients with chronic kidney disease are limited, and no randomized controlled trials have been conducted to test the safety of metformin in patients with significantly impaired kidney function. Population-based studies demonstrate that metformin may be prescribed counter to prevailing guidelines suggesting a renal risk in up to 1 in 4 patients with type 2 diabetes mellitus--use which, in most reports, has not been associated with increased rates of lactic acidosis. Observational studies suggest a potential benefit from metformin on macrovascular outcomes, even in patients with prevalent renal contraindications for its use.

CONCLUSIONS AND RELEVANCE

Available evidence supports cautious expansion of metformin use in patients with mild to moderate chronic kidney disease, as defined by estimated glomerular filtration rate, with appropriate dosage reductions and careful follow-up of kidney function.

Metformin-associated lactic acidosis in Chinese patients with type II diabetes

Metformin is a widely used antidiabetic agent that is generally considered safe. However, metformin-associated lactic acidosis (MALA), though not common, occurs from time to time and results in significantly high mortality. A series of 23 MALA cases in a local major hospital in Hong Kong is reported in this article to demonstrate the epidemiological data, risk factors, clinical features as well as the clinical outcomes for better understanding of this disease entity. It is the first MALA case series in which plasma metformin levels were assessed. However, the results show that plasma metformin levels in MALA bear no diagnostic and prognostic values. Risk factors of mortality were identified as shock and high plasma lactate levels. The majority of patients were found to have significantly raised creatinine versus a normal baseline value before the acute illness. Concomitant illnesses taking place alongside MALA were common. With a high utility rate of renal replacement therapy (82.6%) in the study group, the mortality rate was 30.4%.

Assessing the appropriate use of metformin in an inpatient setting and the effectiveness of two pharmacy-based measures to improve guideline adherence

OBJECTIVE

To demonstrate the level of compliance to metformin-prescribing guidelines and to evaluate the effectiveness of 2 pharmacy-based interventions.

METHODS

Retrospective chart review of all inpatients who had received at least 2 doses of metformin while hospitalized. Two cohorts of patients had chart audits-one group (group A) hospitalized between March and August of 2003 (487 patients) and one group (group B) hospitalized between August of 2005 and January of 2006 (370 patients). In December of 2003, the pharmacy inserted a safety alert in the electronic ordering system and mailed a printed safety alert to all clinical staff outlining the contraindications and precautions concerning metformin use.

RESULTS

More than two-thirds (69.3%) of the charts reviewed demonstrated that metformin was used in accordance with the prescribing guidelines. Surgical procedures, intravenous contrast use, and elevated serum creatinine levels accounted for the greatest percentage of guideline violations. The prescribing guidelines were violated 27.4% (47/137 charts) of the times in group A and 34.3% (40/146 charts) of the times in group B.

CONCLUSIONS

The significance of this study is that metformin is often given in spite of the presence of contraindications to its use. Two pharmacy interventions were ineffective in decreasing the guideline violation frequency in a group of patients who were prescribed the drug.