http://bmj.com/cgi/content/full/324/7348/1236
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 Collections under
which this article appears: Diabetes
Adverse
drug reactions |
David Spurgeon Quebec
Metformin, the most commonly prescribed branded diabetes drug in the United States, may often be inappropriately prescribed for patients with type II diabetes who have renal dysfunction and congestive heart failure, where it has been associated with lactic acidosis causing death.
This is the finding of a group of pharmacists and public health doctors, which they report in a research letter to the editor of JAMA (2002;287:2504-5).
They did a retrospective review of randomly selected charts of patients receiving metformin (Glucophage) through the outpatient pharmacy at an academic medical centre between 1 January and 30 September 2000.
They considered patients to have had congestive heart failure if that diagnosis was in their records and if they were taking drugs for it, while patients with renal dysfunction were defined as having a serum creatinine concentration >1.5 mg/dl (132.6 m mol/l) for men and >1.4 mg/dl (123.8 m mol/l) for women. They also reviewed records for documentation of functional cardiac status or evidence that contraindications were considered.
The researchers found 241 patients with two or more prescriptions for metformin, and 100 of these were randomly selected for chart review. Of these patients 22 were found to have either congestive heart failure requiring treatment or renal insufficiency: 14 had congestive heart failure only, five had renal insufficiency only, and three had both. In only two cases did documentation show that contraindications for metformin were considered.
Thus almost a quarter of the patients whose records were seen had one or more absolute contraindications, a finding that the researchers say resembles similar rates of inappropriate metformin prescribing in several recent European studies.
A 1999 risk benefit assessment indicated that the incidence of lactic acidosis associated with metformin is between 1 in 10 000 and 1 in 100 000 patient years. But in the first 14 months after the drug’s release in the United States, the Food and Drug Administration received notification of 47 confirmed cases, with a 42% death rate. More than 90% of these patients had relative or absolute contraindications to metformin.
The researchers say their assessment may underestimate the frequency of contraindications to metformin. Although the drug contains a "black box" warning in the package insert, it is difficult to determine whether doctors are aware they are prescribing metformin against this warning. The researchers’ results show that the drug may often be inappropriately prescribed despite the warning.
"Documentation of this potential risk in the medical record is limited and
health care providers should consider improving the documentation of the risk of
lactic acidosis and provide appropriate counselling for patients who receive the
drug," they conclude.
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Collections under
which this article appears:Diabetes
Adverse
drug reactions |
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