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 [scored]: 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.