Patients are still dying as a result of methotrexate dosage errors, although the risk has been known for a long time and these errors are avoidable.

Methotrexate is a cytotoxic drug used in oncology, rheumatology and dermatology. Its adverse effects, which can sometimes be serious or even fatal, affect various organs. The higher the dose, the stronger the adverse effects, which are exacerbated in case of renal failure. Disorders such as a fever and oral ulceration can indicate adverse effects.

Since the 1980s, hundreds of cases of serious adverse effects caused by this drug have been reported around the world, including dozens of fatal cases, often as a result of dosage errors. The errors can occur in the doctor’s prescription, the pharmacist’s dispensing or the dose taken by the patient. Many drugs have to be taken daily, but a small dose of methotrexate administered only once a week is sufficient for the treatment to be effective. The most common error is for the weekly oral dose of methotrexate to be taken daily, leading to a major overdose.

To prevent these potentially fatal errors, it is important to decide upon a fixed day of the week for administering the drug, and for that day to be specified on the prescription, written by the pharmacist on the package and on an index card maintained by the patient.

©Prescrire May 2007

Source: "Méthotrexate par voie orale : prévenir les surdoses par erreur" Rev Prescrire 2007 ; 27 (283) : 352-355.
"Oral methotrexate: preventing avoidable overdose" Prescrire Int 2007 ; 16 (90) : 150-152.

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