Low dose methotrexate: Introduction

Last updated: June 12, 2020

This is Li. He is 65 years old and has been suffering with a fever, shortness of breath and cough for ten days. He attends his local walk-in centre and is prescribed amoxicillin 500mg three times a day for a presumed community acquired pneumonia.

One week later he presents to the Emergency Department with haematuria, bloody diarrhoea, fever and oral mucosal ulceration. Laboratory tests reveal pancytopenia and moderate renal impairment (CrCl 40ml/min). His liver function tests are all within range.

His history includes psoriasis for which he is prescribed low dose methotrexate (7.5mg weekly) and folic acid (5mg weekly), and chronic kidney disease.

Acute methotrexate toxicity is suspected and the drug is suspended. After prompt treatment with rescue intravenous folinic acid, blood transfusions and antibiotics, Li recovers and is discharged.

Low dose methotrexate is an effective regimen for a range of indications but fatalities have been reported.

  What risk factors does Li have for developing acute methotrexate toxicity?
  What can be done to mitigate the risk of serious side effects in patients taking low dose methotrexate?

The answers to these two questions form the learning outcomes for this tutorial. It should only take 10 minutes or so to read. You will probably already know a lot of it, but this is an opportunity to consolidate your knowledge. 

Patients must be appropriately monitored during treatment so that signs of possible toxic effects or adverse reactions can be detected and evaluated with minimal delay.

- Pfizer prescribing information (SmPC)

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