Allopurinol + azathioprine/mercaptopurine — myelosuppression
- Allopurinol blocks xanthine oxidase
- thiopurine inactivation falls
- 6-MP exposure rises → myelosuppression
- Avoid; or use ~25–33% thiopurine dose
- Monitor CBC closely
- Classic: allopurinol + azathioprine
Interaction at a glance
- 6-MP exposure rises → myelosuppression
- Avoid; or use ~25–33% thiopurine dose
Mechanism
- Allopurinol blocks xanthine oxidase
- thiopurine inactivation falls
- Classic: allopurinol + azathioprine
Clinical consequence
- 6-MP exposure rises → myelosuppression
Monitoring
- Avoid; or use ~25–33% thiopurine dose
- Monitor CBC closely
Self-check
- If allopurinol must be combined with a thiopurine, what dose is typically used?
About 25–33% of the usual thiopurine dose.
- What should be monitored closely with allopurinol + a thiopurine?
CBC.
- What major toxicity can result from allopurinol + a thiopurine?
Myelosuppression.
Drugs in this interaction (3)
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