All areas of clinical practice · UKMLA & AKT
Drug-induced blood dyscrasias
A free high-yield preview for the UKMLA Applied Knowledge Test. Below are the key points to recognise drug-induced blood dyscrasias — the full SA Note notes add investigations, management, complications and 10 practice questions.
Key high-yield points
- Direct toxicity - dose-dependent bone marrow suppression (e.g. methotrexate, cytotoxics)
- Immune-mediated - idiosyncratic, dose-independent (e.g. carbimazole agranulocytosis, penicillin thrombocytopenia)
- Redistribution - prednisolone causes neutrophilia by demarginating neutrophils from endovascular wall + releasing band neutrophils from marrow reserve; not a sign of toxicity
- TPMT pathway - azathioprine → 6-mercaptopurine → inactivated by TPMT; TPMT deficiency (~1 in 200-300) causes 6-TGN accumulation → pancytopenia
TPMT activity must be checked before starting azathioprine or mercaptopurine. Homozygous deficiency = contraindicated. Heterozygous (intermediate, ~10% population) = reduced dose + close monitoring.
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