Low serum level and chronic toxicity for methotrexate. Case Report

Methotrexate (MTX) is a folic acid antagonist used to treat different immunological or proliferative illnesses because of its anti-proliferative and anti-inflammatory effects. MTX Toxicity is considered a severe problem. Although acute toxicity related to high-dose administration (doses ≥500 mg/m²) can be predicted based on the given dose, chronic toxicity still has no specific factors to predict it, so treatment depends on the history and symptoms of toxicity. MTX was initially used for oncology indications with high cyclic doses, then expanded to non-oncology indications with different low doses and frequencies. This significant change in doses resulted in dosing errors that contributed to MTX toxicity reports. Measures to prevent the toxicity of MTX should be implemented.

A 66-year-old female patient ingested 10 mg of MTX daily for one month instead of the once-toxicity symptoms. The serum level of MTX was requested, and treatment with folinic acid was initiated until the patient improved with the discontinuation of MTX.

There is limited literature about the lack the total cumulative dose, duration of intake, or serum level of MTX. All this information was provided in this case report, but drug-drug interactions were not reviewed, although aspirin and pantoprazole were identified as having interactions with methotrexate in this patient. Minimum total cumulative dose identification may help assess the toxicity risk in such patients.

Low-dose MTX chronic toxicity still needs further information to guide the patient's risk of toxicity and when to initiate treatment. Safety-practical measures should be implemented to prevent such administration errors.