What is the method of action of Methotrexate?

antimetabolite that inhibits dihydrofolate reductase

an enzyme essential for the synthesis of purines and pyrimidines

What is the main clinical use of Methotrexate?

• inflammatory arthritis, especially rheumatoid arthritis
• psoriasis
• some chemotherapy acute lymphoblastic leukaemia

What are the main adverse effects of Methotrexate?

• mucositis
• myelosuppression
• pneumonitis (the most common pulmonary manifestation)
• pulmonary fibrosis
• liver fibrosis

How does Methotrexate induced pneumonitis present?

non-productive cough, dyspnoea, malaise, fever

What is the advise regarding pregnancy and Methotrexate?

• women should avoid pregnancy for at least 6 months after treatment has stopped
• need to use effective contraception for at least 6 months after treatment

What are the most important drug interactions with Methotrexate?

• avoid prescribing trimethoprim or co-trimoxazole concurrently - increases risk of marrow aplasia
• high-dose aspirin increases the risk of methotrexate toxicity secondary to reduced excretion

What is the treatment for Methotrexate toxicity?

folinic acid