Table 3.

Recommendations to the prescribing physician for mercaptopurines

Table. Message to prescriber based on phenotype call
Phenotype	Mercaptopurine	Azathioprine	Thioguanine
Extensive Metabolizer	The patient is considered an extensive or normal metabolizer of mercaptorpurine. No dose reductions from the usual starting dose are recommended. Subsequent dose adjustments should be made at 2 week intervals and based on disease-specific guidelines. For myelosuppression, no special emphasis on reducing MP doses is necessary.	The patient is considered an extensive or normal metabolizer of azathioprine. No dose reductions from the usual starting dose are recommended. Subsequent dose adjustments should be made at 2 week intervals and based on disease-specific guidelines.	The patient is considered an extensive or normal metabolizer of thioguanine. No dose reductions from the usual starting dose are recommended. Subsequent dose adjustments should be made at 2 week intervals and based on disease-specific guidelines. For myelosuppression, no special emphasis on reducing TG doses is necessary.
Intermediate Metabolizer	The patient is considered an intermediate metabolizer for mercaptopurine. Initiate therapy at 30 to 70% of the usual starting dose. Subsequent dose adjustments should be made at 2 – 4 week intervals and based on disease-specific guidelines. If myelosuppression occurs, reducing the MP dose should be considered before reducing the doses of other myelosuppresive agents.	The patient is considered an intermediate metabolizer for azathioprine. Consider initiating therapy at 30 to 70% of the usual starting dose. Subsequent dose adjustments should be made at 2 – 4 week intervals and based on disease-specific guidelines.	The patient is considered an intermediate metabolizer for thioguanine. Consider initiating therapy at 50 to 70% of the usual starting dose. Subsequent dose adjustments should be made at 2 – 4 week intervals and based on disease-specific guidelines. If myelosuppression occurs, reducing the TG dose should be considered before reducing the doses of other myelosuppresive agents.
Poor Metabolizer	The patient is considered a poor metabolizer for mercaptopurine. When used for cancer treatment: Significant, dose adjustments are required. Initiate therapy at 10% of the usual starting dose and decrease the frequency to three times per week. Subsequent dose adjustments should be made at 4 – 6 week intervals and based on disease-specific guidelines. If myelosuppression occurs, reducing the MP dose should be considered before reducing the doses of other myelosuppresive agents. When used for non-malignant conditions: Consider alternative therapy before using MP.	The patient is considered a poor metabolizer for azathioprine. Consider alternative therapy. If azathioprine must be used, significant dose adjustments are required. Initiate therapy at 10% of the usual starting dose and decrease the frequency to three times per week. Subsequent dose adjustments should be made at 4 – 6 week intervals and based on disease-specific guidelines.	The patient is considered a poor metabolizer for thioguanine. Consider alternative therapy. If TG must be used, significant dose adjustments are required. Initiate therapy at 10% of the usual starting dose and decrease the frequency to three times per week. Subsequent dose adjustments should be made at 4 – 6 week intervals and based on disease-specific guidelines. If myelosuppression occurs, reducing the TG dose should be considered before reducing the doses of other myelosuppresive agents
Not Determined	A DMET test result has been found in the patient’s record; however, the patient’s TPMT genotype or phenotype was not defined. Routine clinical criteria should be used to determine the patient’s starting dose. Dose reductions are recommended in patients who have at least one dysfunctional TPMT-deficient allele. The DMET results report can be found under the RESULTS Tab -> OUTSIDE RESULTS. Please consult your clinical pharmacy specialist or the Drug Information Center (301-496-2407) for assistance with dosing.	A DMET test result has been found in the patient’s record; however, the patient’s TPMT genotype or phenotype was not defined. Routine clinical criteria should be used to determine the patient’s starting dose. Dose reductions are recommended in patients who have at least one dysfunctional TPMT-deficient allele. The DMET results report can be found under the RESULTS Tab -> OUTSIDE RESULTS. Please consult your clinical pharmacy specialist or the Drug Information Center (301-496-2407) for assistance with dosing.	A DMET test result has been found in the patient’s record; however, the patient’s TPMT genotype or phenotype was not defined. Routine clinical criteria should be used to determine the patient’s starting dose. Dose reductions are recommended in patients who have at least one dysfunctional TPMT-deficient allele. The DMET results report can be found under the RESULTS Tab -> OUTSIDE RESULTS. Please consult your clinical pharmacy specialist or the Drug Information Center (301-496-2407) for assistance with dosing.
Not Poor Metabolizer	The patient’s phenotype could not be determined to a single phenotype; however, the patient is NOT a poor metabolizer. Use routine clinical and patient-specific factors to determine dose. Dose reductions are recommended in patients who have at least one dysfunctional TPMT-deficient allele. The DMET results report can be found under the RESULTS Tab -> OUTSIDE RESULTS. Please consult your clinical pharmacy specialist or the Drug Information Center (301-496-2407) for assistance with dosing.	The patient’s phenotype could not be determined to a single phenotype; however, the patient is NOT a poor metabolizer. Use routine clinical and patient-specific factors to determine dose. Dose reductions are recommended in patients who have at least one dysfunctional TPMT-deficient allele. The DMET results report can be found under the RESULTS Tab -> OUTSIDE RESULTS. Please consult your clinical pharmacy specialist or the Drug Information Center (301-496-2407) for assistance with dosing.	The patient’s phenotype could not be determined to a single phenotype; however, the patient is NOT a poor metabolizer. Use routine clinical and patient-specific factors to determine dose. Dose reductions are recommended in patients who have at least one dysfunctional TPMT-deficient allele. The DMET results report can be found under the RESULTS Tab -> OUTSIDE RESULTS. Please consult your clinical pharmacy specialist or the Drug Information Center (301-496-2407) for assistance with dosing.