PEBC MCQ Prescription Review & Dispensing question: mg daily after a kidney condition

PEBC MCQPrescription Review & Dispensing

TF, 64, takes allopurinol 300 mg daily. A new prescription arrives for azathioprine 100 mg daily after a kidney condition was diagnosed. Which of the following is the main concern?

a. There is no interaction, as the drugs act on different organs
b. Azathioprine raises uric acid, so the allopurinol dose should be doubled
c. Allopurinol speeds azathioprine elimination, reducing its effect
d. Allopurinol raises azathioprine levels, risking marrow suppression

Show the answer and explanation

Answer: d. Allopurinol raises azathioprine levels, risking marrow suppression

Allopurinol inhibits xanthine oxidase, a major pathway for inactivating azathioprine's active metabolite 6-mercaptopurine. Combined use can cause life-threatening bone marrow suppression unless the azathioprine dose is reduced to about one-quarter with close CBC monitoring, or an alternative is used. The prescriber must be contacted before dispensing. Source: Azathioprine (Imuran) product monograph, Drug interactions: allopurinol (DPD, checked 2026); allopurinol product monograph (checked 2026).

Common mistake

Missing the allopurinol-azathioprine interaction.

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Original practice material written to the public PEBC blueprint; not a past or real exam question. Not affiliated with or endorsed by The Pharmacy Examining Board of Canada (PEBC). Educational practice material for exam preparation only. Not medical advice and not a substitute for current product monographs, clinical guidelines or professional judgement. Questions have not yet been reviewed by a licensed pharmacist.