Overview of Methotrexate Toxicity: A Comprehensive Literature Review

Methotrexate (MTX) is significantly more effective than and has a considerable advantage over placebo in patients with severe and persistent rheumatoid arthritis (RA). The drug is used to treat a variety of malignant disorders (leukemia and cancer of the lung, breast, and uterus) and ectopic pregnancy. As its side effects are outweighed by its effectiveness, MTX is a first-line antirheumatic drug in many countries. MTX is found in extracellular compartments, such as the synovium, as well as other organs, such as the kidney and liver. To improve treatment, increase adherence, and decrease mortality in MTX therapy, it is essential to reduce its toxicity and understand its side effects. Therefore, this comprehensive review was conducted to assist physicians and researchers in better understanding the toxicity of MTX and how to deal with this toxicity. MTX is eliminated via the kidneys, which are capable of excretion and reabsorption within the renal tubules. Although higher doses of MTX (known as high-dose MTX (HD-MTX), defined as doses of 500 mg/m² or greater) are often more beneficial, they can produce toxicity and side effects such as bone marrow suppression, pulmonary toxicity, nephrotoxicity, hematologic toxicity, and an increased risk of infections. Treatment of severe MTX toxicity has three main goals: clearance of MTX from the bloodstream, folinic acid therapy, and organ treatment. Leucovorin is highly beneficial in preventing myelosuppression, gastric toxicity, and neurotoxic effects after HD-MTX therapy. The preferred antidote for MTX poisoning is folinic acid. Glucarpidase has been licensed for the treatment of high plasma MTX levels of >1 μmol/L in patients with compromised renal function who have delayed MTX elimination. In patients with renal deficiency, a lower initial dose is considered with an estimated glomerular filtration rate (eGFR) between 30 and 59 mL/minute. These patients need to be monitored, and a more gradual dosage increase and a lower weekly maximum should be considered regarding their general health situation. MTX is contraindicated in patients with RA if the eGFR is <30 mL/minute.