TPMT metabolizes thiopurine drugs used in leukemia treatment and autoimmune diseases. Variants in TPMT can lead to severe bone marrow toxicity if dosing isn't adjusted.
Intermediate Metabolizer
Drug
Azathioprine
Effect
Myelosuppression risk (intermediate)
Recommendation
ADJUST. Standard dose with close monitoring.
CPIC Guideline
CPIC Level B
FDA Label
Monitor CBC closely
Poor Metabolizer
Drug
Azathioprine
Effect
Increased thioguanine nucleotides → severe myelosuppression
Recommendation
AVOID or reduce dose by 90%.
CPIC Guideline
CPIC Level A
FDA Label
Black box warning: test before use
Poor Metabolizer
Drug
Mercaptopurine
Effect
Severe myelosuppression risk
Recommendation
AVOID or reduce dose by 90%.
CPIC Guideline
CPIC Level A
FDA Label
Black box warning: test before use
Clinical Action: These recommendations are based on CPIC guidelines and FDA labeling. Discuss results with your healthcare provider or genetic counselor to determine appropriate treatment adjustments.
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