Cancer drugs: mechanism & toxicity flashcards
8 high-yield MRCP Part 1 cards from the Intellect Medicos Haematology & Oncology course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.
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What is the mechanism of methotrexate, and what is the antidote in toxicity?
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Dihydrofolate reductase inhibitor; folinic acid (calcium folinate) rescue.
Why? Blocking DHFR depletes the tetrahydrofolate needed for DNA synthesis; folinic acid bypasses the block.
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Name three major toxicities of cisplatin.
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Any three of: nephrotoxicity, ototoxicity, peripheral neuropathy, hypomagnesaemia, severe nausea and vomiting.
Why? Platinum compounds cross-link DNA; they accumulate in the kidney, inner ear and nerves.
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Before starting 5-fluorouracil or capecitabine, which enzyme deficiency must be tested for?
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Dihydropyrimidine dehydrogenase (DPD) deficiency.
Why? DPD breaks down fluoropyrimidines; deficient patients can get severe or fatal toxicity (mucositis, diarrhoea, neutropenia).
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Trastuzumab targets which receptor, and what is its key toxicity?
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HER2; cardiotoxicity (fall in LVEF / heart failure) — monitor LVEF.
Why? It is used in HER2-positive breast and gastric cancer. Unlike anthracycline damage, the cardiac dysfunction is usually reversible on stopping.
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What is the first-line treatment of a significant immune-related adverse effect (e.g. colitis or pneumonitis) from a checkpoint inhibitor such as pembrolizumab?
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Withhold the drug and give high-dose corticosteroids.
Why? PD-1/PD-L1 and CTLA-4 inhibitors release the brakes on T cells, which can then attack normal tissues.
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Which two serious risks are increased by tamoxifen?
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Endometrial cancer and venous thromboembolism.
Why? Tamoxifen is a selective oestrogen receptor modulator: an antagonist in the breast but a partial agonist in the endometrium and liver.
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What is the mechanism of action of hydroxycarbamide (hydroxyurea)?
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It inhibits ribonucleotide reductase, blocking DNA synthesis.
Why? It is used for cytoreduction in PV, ET and CML and to raise HbF in sickle cell disease.
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A patient taking azathioprine is started on allopurinol for tumour lysis prophylaxis. What is the risk?
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Severe azathioprine (6-mercaptopurine) toxicity with bone marrow suppression — avoid the combination or cut the azathioprine dose to a quarter.
Why? Allopurinol inhibits xanthine oxidase, which normally inactivates 6-mercaptopurine.