Based on TPMT status, for malignancy, start with drastically reduced doses (reduce daily dose by 10-fold and reduce frequency to thrice weekly instead of daily, e.g., 10 mg/m2/day given just 3 days/week) and adjust doses of mercaptopurine based on degree of myelosuppression and disease-specific guidelines. Allow 4-6 weeks to reach steady-state after each dose adjustment. If myelosuppression occurs, emphasis should be on reducing mercaptopurine over other agents. For non-malignant conditions, consider alternative non-thiopurine immunosuppressant therapy (PMID 20354201, 1960624, 11302950, 16530532). NUDT15 phenotype could not be assigned based on genotyping. If thiopurines are required and either TPMT or NUDT15 status is unknown, monitor closely for toxicity.