Names and pronunciation
(mer-kap-toe-pyoor′een) Purinethol, Purixan
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Drug reference
(mer-kap-toe-pyoor′een) Purinethol, Purixan
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Func. class.: Antineoplastic- antimetabolite
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Chem. class.: Purine analog
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Do not confuse: purinethol/propylthiouracil
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ACTION: Inhibits purine metabolism at multiple sites, which inhibits DNA and RNA synthesis; specific for S phase of cell cycle
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USES: Acute lymphocytic leukemia in combination Unlabeled uses: Crohn’s disease, ulcerative colitis
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CONTRAINDICATIONS: Preg- nancy, breastfeeding, patients with prior product resistance, hypersensitivity Precautions: Renal/hepatic disease, tumor lysis syndrome, dental disease, herpes, radiation therapy, leukopenia, thrombocytopenia, anemia, requires an experienced clinician, secondary malignancy, infection, hypocalcemia, hyperuricemia, hyperphosphatemia, hyperkalemia
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SIDE EFFECTS GI: Nausea, vomiting, anorexia, diar- rhea, stomatitis, hepatotoxicity (high doses), jaundice, gastritis, pancreatitis GU: Hyperuricemia HEMA: Thrombocytopenia, leukopenia, myelosuppression, anemia INTEG: Rash, dry skin, urticaria, alopecia
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INTERACTIONS Increase: effects of mercaptopurine— allopurinol; avoid use or decrease dose by at least 25% Increase: effects—radiation or other antineoplastics, immunosuppressants Increase: bone marrow suppresion— azaTHIOprine, sulfamethoxazole-trimeth oprim; avoid concurrent use or monitor blood counts Increase: anticoagulant action—antico- agulants, NSAIDs, thrombolytics, platelet inhibitors, salicylates; monitor PT, INR Decrease: antibodies—live virus vaccines; bring vaccinations up-to-date before use Decrease: TPMT, rapid bone marrow sup- pression—balsalazide, olsalazine, mesa- lamine, sulfaSALAzine; use cautiously Drug/Lab Test Increase: alk phos, bilirubin, uric acid Decrease: platelets, WBC, RBC
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DOSAGE AND ROUTES Acute lymphocytic leukemia • Adult/child: PO 1.5-2.5 mg/kg/day in combination with other agents; start mer- captopurine therapy after a complete he- matologic remission Renal dose • Adult: PO CCr <50 mL/min, give dose q48hr; if used with allopurinol, reduce usual dose by at least 25% Crohn's disease (unlabeled) Adult/child ≥3 yr PO 0.75-1.5 mg/kg/day Ulcerative colitis (unlabeled) Adult PO 1.5 mg/kg/day Child ≥3 yr PO 1-1.5 mg/kg/day
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Available forms: Tabs 50 mg; oral susp 20 mg/mL
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Administer: • Store in tightly closed container in cool environment • Give product after evening meal, be- fore bedtime, on an empty stomach; risk of relapse is lower with evening dose • Use cytotoxic handling procedures • Suspension: Shake well; wash syringe with warm, soapy water; rinse; move plunger up and down several times; use only after dry; after opening, use within 6 wk
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Assess: • Bone marrow suppression: CBC, dif- ferential, platelet count weekly during in- duction and monthly during maintenance; withhold product at first sign of abnor- mally large decrease in blood counts un- less bone marrow aplasia is the goal • Thiopurine methyltransferase (TPMT) deficiency: individuals are prone to rapid bone marrow suppression; dosage reduc- tion may be required in homozygous TPMT– deficient persons M • Tumor lysis syndrome: monitor for increased potassium, uric acid, phos- phate; decreased urine output, calcium • Renal studies: BUN, serum uric acid, urine CCr, electrolytes before, during therapy • I&O ratio; report fall in urine output to <30 mL/hr; increase fluids to 3 L/day unless contraindicated • Monitor temperature; fever may indi- cate beginning infection; no rectal tem- perature • Hepatotoxicity: hepatic studies be- fore, during therapy: bilirubin, alk phos, AST, ALT weekly during beginning ther- apy; hepatic encephalopathy, toxic hepa- titis, ascites can be fatal; monitor for jaundice, dark urine, clay-colored stools, abdominal pain; reversible after comple- tion of treatment • Bleeding: hematuria, guaiac, bruising, petechiae, mucosa, or orifices; avoid IM inj if platelets are <100,000/mm3; blood transfusions may be needed • Stomatitis: buccal cavity for dryness, sores, ulceration, white patches, oral pain, bleeding, dysphagia • Increase fluid intake to 2-3 L/day to prevent urate deposits, calculi formation, unless contraindicated • Rinsing of mouth tid-qid with water, club soda; brushing of teeth bid-tid with soft brush or cotton-tipped appli- cators for stomatitis; use unwaxed den- tal floss • Pregnancy/breastfeeding: identify whether pregnancy is planned or sus- pected, or if breastfeeding; do not use in pregnancy or for 6 mo after last dose or breastfeeding, excreted in breast milk
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Evaluate: • Therapeutic response: decreased size of tumor, spread of malignancy
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CLINICAL CONSIDERATIONS
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Patient and caregiver information: • To avoid foods with citric acid, hot temperature, or rough texture for stoma- titis; to report stomatitis: any bleeding, white spots, ulcerations in mouth; to ex- amine mouth daily, report symptoms • To drink 10-12 8-oz glasses of fluid/day • To notify prescriber of fever, chills, sore throat, nausea, vomiting, anorexia, diar- rhea, bleeding, bruising, all of which may indicate blood dyscrasias/infection • To report signs of infection: fever, sore throat, flulike symptoms • To report signs of anemia: fatigue, headache, faintness, SOB, irritability • To report bleeding; to avoid use of ra- zors, commercial mouthwash • To avoid use of aspirin products, NSAIDs • To take entire dose at one time; how to safely handle and dispose of product • Pregnancy/breastfeeding: that contra- ceptive measures are recommended dur- ing therapy and for 6 mo after last dose, not to breastfeed
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PHARMACOKINETICS Incompletely absorbed when taken orally, metabolized in liver, excreted in urine, peak 1-2 hr, terminal half-life 47 min (adult), 21 min (child)
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• Adult/child: PO 1.5-2.5 mg/kg/day in combination with other agents; start mer- captopurine therapy after a complete he- matologic remission Renal dose
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