All areas of clinical practice · UKMLA & AKT
Drug-induced blood dyscrasias
A free high-yield preview for the UKMLA Applied Knowledge Test, covering how to recognise this condition. The full SA Note notes add investigations, management and complications, with practice questions on this topic.
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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