Mercaptopurine Disease Interactions

Because of their cytotoxic effects on rapidly proliferating tissues, antineoplastic agents frequently can, to varying extent, induce myelosuppression. The use of these drugs may be contraindicated in patients with known infectious diseases. All patients should be instructed to immediately report any signs or symptoms suggesting infection such as fever, sore throat, or local infection during antineoplastic therapy. Close clinical monitoring of hematopoietic function is recommended.

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Mercaptopurine is hepatotoxic. Hepatic injury can occur at any dosage, however, increased frequency of injury occurs when doses exceed 2.5 mg/kg/day. Deaths due to hepatic necrosis have been reported. Patients should be instructed to immediately report any signs of hepatotoxicity such as jaundice, hepatic dysfunction such as, jaundice, dark urine, right upper quadrant pain, or anorexia. Therapy with mercaptopurine should be administered cautiously in patients with or predisposed to compromised hepatic function. Clinical monitoring of hepatic function and determination of the etiology of hepatic dysfunction is recommended.

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Mercaptopurine induces dose-related myelosuppression which can be delayed. Leukopenia, thrombocytopenia, and anemia have been reported during mercaptopurine therapy. Therapy should be administered cautiously in patients with myelosuppression and therapy should be withheld at the first indication of an abnormally large reduction of any bone marrow element. Patients should be instructed to immediately report any signs or symptoms suggesting bone marrow suppression such as fever, sore throat, local infection, or bleeding. Close monitoring of hematopoietic function is recommended.

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Thioguanine is closely related structurally and functionally to mercaptopurine. A rare deficiency in the enzyme thiopurine methyltransferase (TMPT) results in an increased sensitivity to the myelosuppressive effects of both drugs causing rapid bone marrow suppression following initial mercaptopurine or thioguanine administration. Therapy with thioguanine or mercaptopurine should be administered cautiously and at a reduced dose in patients with TMPT deficiency.

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Mercaptopurine is excreted in the urine as unchanged drug and metabolites. Renal elimination may be reduced in patients with impaired renal function. Therapy with mercaptopurine should be initiated at a reduced dosage in patients with compromised renal function. Clinical monitoring of renal function is recommended.

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