Oral methotrexate: preventing avoidable overdose.
(1) Even though the risk has been known since the 1980s, healthcare professionals and patients in many countries still make mistakes involving weekly oral methotrexate therapy. (2) The adverse effects of methotrexate, some of which can be life-threatening, mainly affect haematopoiesis, the kidneys, liver, gastrointestinal tract, skin and mucosa, and lungs. They can occur at low doses, are dose-dependent, and can be precipitated by renal failure or drug interactions. (3) Manifestations of adverse reactions include fever and mouth ulceration. (4) Adverse effects can be due to improper drug administration. (5) Oral methotrexate overdose is linked to errors in prescription, dispensing or administration. It often involves mistakenly taking a weekly dose daily. (6) These errors are preventable. Patients must be informed that methotrexate tablets should be taken weekly: the treatment day should be chosen with the patient when the prescription is written, and this information should be specified on the prescription. It should then be copied onto the box when the drug is dispensed, and also onto an individual treatment register. For additional safety, drug packaging should also contain information that reinforces these measures.