Chemotherapy Drug Toxicities
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Direct answer
Chemotherapy drug toxicities follow predictable drug and organ pairs that examinations test as recall: doxorubicin with the heart, bleomycin with the lungs, cisplatin with the kidneys and ears, and cyclophosphamide with the bladder. Each pair has a preventive or rescue agent, such as dexrazoxane for anthracycline cardiotoxicity, mesna for haemorrhagic cystitis and leucovorin for high-dose methotrexate. Recognising the pair is usually enough to answer the question.
What you must remember
- Doxorubicin: Cumulative, dose-related cardiomyopathy, with risk rising beyond roughly 450 to 550 mg/m²; dexrazoxane is used for cardioprotection in selected patients, and extravasation causes severe local necrosis.
- Bleomycin: Pneumonitis progressing to pulmonary fibrosis, with risk climbing above roughly 400 units cumulative; skin hyperpigmentation and mucocutaneous reactions are also characteristic.
- Cisplatin: Dose-limiting nephrotoxicity, magnesium wasting, ototoxicity and vomiting; prevented by hydration and magnesium replacement.
- Cyclophosphamide and ifosfamide: Haemorrhagic cystitis from the metabolite acrolein; mesna is the uroprotective agent, and ifosfamide adds encephalopathy and Fanconi-type tubular damage.
- Methotrexate: Mucositis, myelosuppression and renal tubular precipitation at high dose; leucovorin rescue is standard, with glucarpidase when clearance is delayed in renal impairment.
- Vincristine: Peripheral and autonomic neuropathy with constipation and paralytic ileus; intrathecal administration is fatal, so the route is a safety-critical fact.
- Fluoropyrimidines: Severe toxicity in dihydropyrimidine dehydrogenase deficiency; uridine triacetate is the antidote for overdose, ideally given within 96 hours.
Worked scenario: a young man on ABVD
A 26-year-old man with Hodgkin lymphoma starts the ABVD regimen, which contains doxorubicin, bleomycin, vinblastine and dacarbazine.
- Check the heart at baseline: A baseline echocardiogram is recorded, because doxorubicin damage is cumulative and a reduced ejection fraction changes the plan.
- Check the lungs at baseline: Pulmonary function with diffusing capacity is recorded, since bleomycin pneumonitis can appear late and is easily mistaken for infection.
- Monitor during treatment: The team watches for dyspnoea, a dry cough and a fall in gas transfer, and reviews the cumulative anthracycline dose at each cycle.
- Consider cardioprotection: Dexrazoxane is considered when the planned cumulative dose is high or cardiac reserve is already reduced, and the decision is revisited with the cardio-oncology team.
- Flag the anaesthetic risk: If an anaesthetist later asks for high inspired oxygen during surgery, the bleomycin history matters, because high oxygen concentrations can precipitate acute lung injury.
The reasoning is to link each drug to its organ and its cumulative risk, rather than memorising a list of adverse effects.
Where the examiner sets the trap
The examiner's traps turn on routes, rescue agents and look-alike drugs.
- Trap: a vincristine dose given by the wrong route Correct: given intrathecally it is fatal, so the drug is given only intravenously, with strict labelling.
- Trap: confusing mesna with the methotrexate rescue agent Correct: mesna protects the bladder, while leucovorin rescues the cells.
- Trap: missing cisplatin ototoxicity Correct: cisplatin causes high-frequency hearing loss, which can be worsened by aminoglycosides.
- Trap: blaming only cyclophosphamide for haemorrhagic cystitis Correct: ifosfamide causes it too and should not be forgotten.
Frequently asked questions
Which chemotherapy agent is most associated with pulmonary fibrosis?
Bleomycin is the chemotherapy agent most associated with pulmonary fibrosis, which can follow pneumonitis and worsens with cumulative dose. Patients may also develop Raynaud-like changes and skin hyperpigmentation. Pulmonary function and diffusing capacity are monitored during treatment.
What is the antidote for high-dose methotrexate toxicity?
Leucovorin, also called folinic acid, is the standard rescue agent for high-dose methotrexate, bypassing the enzyme block to protect normal cells. Glucarpidase is used when methotrexate clearance is delayed, particularly in renal impairment. Urinary alkalinisation and hydration are supportive measures that accompany rescue.
How does mesna prevent haemorrhagic cystitis from cyclophosphamide?
Mesna binds acrolein, the toxic urinary metabolite of cyclophosphamide and ifosfamide, so the bladder lining is protected from its damage. It is given with the chemotherapy dose and in the hours after. Adequate hydration complements its effect in preventing haemorrhagic cystitis.
What agent reduces doxorubicin cardiotoxicity?
Dexrazoxane is the agent used to reduce doxorubicin-induced cardiotoxicity in selected patients, particularly where cumulative anthracycline dosing is high. Cardiotoxicity is itself cumulative and dose-related, so the total dose and baseline cardiac function are recorded. Careful monitoring with echocardiography remains essential.
Why must vincristine never be given intrathecally?
Vincristine given intrathecally causes severe ascending neurological damage and is usually fatal, so the drug is restricted to the intravenous route with strict labelling and safety checks. Intrathecal therapy uses other agents such as methotrexate or cytarabine in the appropriate setting. The route error is a classic safety question in examinations.