Mercaptopurine Warfarin

There are several important drug-drug interactions with allopurinol. The effects of both theophylline and warfarin may be potentiated by allopurinol. Azathioprine and 6-mercaptopurine are purines whose metabolism is inhibited... 

Mercaptopurine [6-MP] (Purinethol) [Antineoplastic/ Antimeta lite] Uses Acute leukemias, 2nd-line Rx of CML NHL, maint ALL in children, immunosuppressant w/ autoimmune Dzs (Crohn Dz) Action Antimetabolite, mimics hypoxanthine Dose Adults. 80-100 mg/mVd or 2.5-5 mg/kg/d maint 1.5-2.5 mg/kg/d Peds. Per protocol X w/ renal/hepatic insuff on empty stomach Caution [D, ] Contra Severe hepatic Dz, BM suppression, PRG Disp Tabs SE Mild hematotox, mucositis, stomatitis, D rash, fever, eosinophilia, jaundice. Hep Interactions T Effects W/ allopurinol T risk of BM suppression W/ trimethoprim-sulfamethoxazole X effects OF warfarin EMS May falsely T glucose OD May cause NA and liver necrosis symptomatic and supportive Meropenem (Merrem) [Antibiotic/Carbapenem] Uses lntra-abd Infxns, bacterial meningitis Action Carbapenem X cell wall synth, a [3-lactam Dose Adults. 1 to 2 g IV q8h Peds. >3 mo, <50 kg 10-40 mg/kg IV q 8h in renal insuff Caution [B, ] Contra [3-Lactam sensitivity Disp Inj 500 mg, 1 g SE Less Sz potential than imipenem D, thrombocytopenia Interactions T Effects W/ probenecid EMS Monitor for signs of electrolyte disturbances and... 

MERCAPTOPURINE ANTICOAGULANTS-WARFARIN Possible 1 anticoagulant effect Induction of metabolism of warfarin Monitor INR closely... 

Azathioprine or mercaptopurine have been sometimes involved in reduced warfarin and acenocoumarol activity, and increased warfarin dosages may be necessary (103). Similar findings were found in a patient taking maintenance phenprocoumon (SEDA-21, 382). 

Spiers AS, Mibashan RS. Letter Increased warfarin requirement during mercaptopurine therapy a new drug interaction. Lancet 1974 2(7874) 221-2. 

Clinically important, potentially hazardous interactions with aminophylline, carbamazepine, cyclosporine, mercaptopurine, methotrexate, phenobarbital, prednisone, vincristine, warfarin... 

ANTICOAGULANTS-ORAL AZATHIOPRINE, MERCAPTOPURINE, MITOTANE Possible i anticoagulant effect induction of metaboiism of warfarin Monitor iNR cioseiy... 

A number of case reports describe an increase in the effects of warfarin, accompanied by bleeding in some cases, caused by an-tineoplastic regimens containing carboplatin, chlormethine, cyclophosphamide, doxorubicin, etoposide, gefitinib, gemcitabine, ifosfamide with mesna, methotrexate, procarbazine, trastuzum-ab, vincristine or vindesine. A decrease in the effects of warfarin has been seen with azathioprine, cyclophosphamide, mercaptop-urine and mitotane, a decrease in the effects of acenocoumarol has been seen with mercaptopurine, and a decrease in the effects of phenprocoumon have l n seen with azathioprine. 

A man well stabilised on warfarin had a marked reduction in his anticoagulant response on two occasions while taking mercaptopurine, but no changes occurred when he took busulfan, cyclophosphamide, cytarab-ine, hydroxycarbamide, mitobronitol, demecolcine or melphalan. A woman needed a marked increase in her dosage of acenocoumarol, from 21 to 70 mg weekly, when she was given mercaptopurine 100 mg daily. Another patient required about a 25% increase in warfarin dose while taking mercaptopurine 1(X) mg daily. 

Martin LA, Mehta SD. Diminished anticoagulant effects of warfarin with concomitant mercaptopurine therapy. Pharmacotherapy (2003) 23, 260-4,... 

Martini A, Jahnchen E, Studies in rats on the mechanisms by which 6-mercaptopurine inhibits the anticoagulant effect of warfarin. J Pharmacol Exp Ther ( 977) 201, 547-53. 

---