Mesalazine monitoring — GPhC CRA MCQ
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Correct answer: A — Thiopurine methyltransferase activity or genotype before the first dose
Absent or very low TPMT activity creates a high risk of profound myelosuppression with standard azathioprine dosing; reduced activity requires substantial dose adjustment. Testing does not replace ongoing FBC, liver and renal monitoring because toxicity can still occur with normal TPMT.
Reference: BNF: azathioprine: https://bnf.nice.org.uk/drugs/azathioprine/