Methotrexate

Question 1

MOA of methotrexate

Answer 1

Antimetabolite that inhibits dihydrofolate reductase- enzyme essential for the synthesis of purines and pyrimidines

Question 2

Indications of methotrexate

Answer 2

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

Question 3

Adverse effects of methotrexate

Answer 3

mucositis
myelosuppression
pneumonitis
pulmonary fibrosis
liver fibrosis

Question 4

Pregnancy and methotrexate

Answer 4

Women should avoid treatment with methotrexate for at least 6 months after treatment has stopped

Question 5

Monitoring of FBC, U+Es and LFTs during methotrexate treatment

Answer 5

Every 2-3 months

Question 6

Interactions of methotrexate

Answer 6

Avoid prescribing trimethoprim or co-trimoxazole concurrently - increased risk of marrow aplasia
High-dose aspirin increases risk of methotrexate toxicity secondary to reduced excretion

Question 7

Prescribing methotrexate

Answer 7

the starting dose of methotrexate is 7.5 mg weekly (source: BNF)
only one strength of methotrexate tablet should be prescribed (usually 2.5 mg)
- folic acid 5mg once weekly should be co-prescribed, taken more than 24 hours after methotrexate dose

Question 8

Treatment for methotrexate toxicity

Answer 8

Folinic acid