MERCAPTOPURINE

Purinethol

DOSE IN ADULTS

Initial: 50 mg daily; may increase by 25 mg/day every 1-2 weeks as tolerated to target dose of 1-1.5 mg/kg/day  Please take on an empty stomach (1 hour before or 2 hours after meals) Dosage adjustment with concurrent allopurinol: Reduce mercaptopurine dosage to 1/4 to 1/3 the usual dose. Dosage adjustment in TPMT-deficiency: reductions are generally required only in homozygous deficiency.

DOSING IN RENAL IMPAIRMENT

Administer every 48 hours

DOSING IN HEPATIC IMPAIRMENT

Decrease Dose

DOSAGE FORMS

Tablet : 50 mg

SIGNIFICANT ADVERSE REACTIONS

Jaundice Leukopenia Drug fever Rash Hyperuricemia Mucositis Oligospermia Opportunistic Infections

CONTRAINDICATIONS

Hypersensitivity to mercaptopurine or any component of the formulation; patients whose disease showed prior resistance to mercaptopurine or thioguanine; severe liver disease, severe bone marrow suppression; pregnancy. Patients on concurrent therapy with drugs which may inhibit TPMT (eg, olsalazine) or xanthine oxidase (eg, allopurinol) may be sensitive to myelosuppressive effects.

DRUG INTERACTIONS

Allopurinol: Can cause increased levels of mercaptopurine by inhibition of xanthine oxidase; decrease dose of mercaptopurine by 75% when both drugs are used concomitantly; may potentiate effect of bone marrow suppression (reduce mercaptopurine to 25% of dose). Aminosalicylates (olsalazine, mesalamine, sulfasalazine): May inhibit TPMT, increasing toxicity/myelosuppression of mercaptopurine. Azathioprine: Metabolized to mercaptopurine, concomitant use may result in profound myelosuppression and should be avoided Hepatotoxic drugs: Any agent which could potentially alter the metabolic function of the liver could produce higher drug levels and greater toxicities from either mercaptopurine or 6-TG. Warfarin: mercaptopurine inhibits the anticoagulation effect of warfarin

PREGNANCY RISK FACTOR — D

LACTATION — Enters breast milk/contraindicated.