Methotrexate Pneumonitis After a Low-Dose Medication Error: A Case Report.

Methotrexate is recommended as the first choice of standard drug therapy following the diagnosis of rheumatoid arthritis. Pneumonitis related to methotrexate is a serious, unpredictable adverse event that may become life-threatening. We reported a case of a 68-year-old woman with rheumatoid arthritis that misunderstood the directions for use and took methotrexate daily, instead of weekly, leading to hepatic, hematological, and pulmonary toxicity.Although the histological evaluation was not performed, patient's clinical presentation, in addition to subsequent investigational findings, supported a diagnosis of pneumonitis resulting from MTX exposure. Toxic dosing over a long period of time along with the concomitant taking of pantoprazole and hypoalbuminemia could have increased the incidence of some adverse events. Concerning pneumonitis related to methotrexate, the toxic dose may have accelerated the pulmonary manifestations, but we do not know if correct dose had been taken, this adverse event would occur. This case enlightened two important issues in rheumatoid arthritis treatment: the possibility of medication errors and the rare, but potentially life-threatening, methotrexate-induced pneumonitis. Improving education and warnings when prescribing and dispensing low-dose methotrexate is essential.