Mercaptopurine

1 INDICATIONS AND USAGE Mercaptopurine is a nucleoside metabolic inhibitor indicated for the treatment of patients with acute lymphoblastic leukemia (ALL) as part of a combination chemotherapy maintenance regimen. ( 1.1 ) 1.1 Acute Lymphoblastic Leukemia Mercaptopurine is indicated for the treatment of patients with acute lymphoblastic leukemia (ALL) as part of a combination chemotherapy maintenance regimen.

12.1 Mechanism of Action Mercaptopurine is a purine analog that undergoes intracellular transport and activation to form metabolites including thioguanine nucleotides (TGNs). Incorporation of TGNs into DNA or RNA results in cell-cycle arrest and cell death. TGNs and other mercaptopurine metabolites are also inhibitors of de novo purine synthesis and purine nucleotide interconversions. Mercaptopurine was cytotoxic to proliferating cancer cells in vitro and had antitumor activity in mouse tumor models. It is not known which of the biochemical effects of mercaptopurine and its metabolites are directly or predominantly responsible for cell death.

2 DOSAGE AND ADMINISTRATION • The recommended starting dosage of mercaptopurine oral suspension is 1.5 mg/kg to 2.5 mg/kg (50 mg/m 2 to 75 mg/m 2 ) orally once daily as part of a combination chemotherapy maintenance regimen. Adjust dose to maintain desirable absolute neutrophil count and for excessive myelosuppression. ( 2.1 ) • Renal Impairment : Use the lowest recommended starting dose or increase the dosing interval. ( 2.3 , 8.6 ) • Hepatic Impairment : Use the lowest recommended starting dose. ( 2.3 , 8.7 ) 2.1 Recommended Dosage The recommended starting dose of mercaptopurine oral suspension is 1.5 mg/kg to 2.5 mg/kg (50 mg/m 2 to 75 mg/m 2 ) orally once daily as part of combination chemotherapy maintenance regimen. Take mercaptopurine oral suspension either consistently with or without food. After initiating mercaptopurine, monitor complete blood counts (CBC) and adjust the dose to maintain absolute neutrophil count (ANC) at a desirable level and for excessive myelosuppression. Evaluate the bone marrow in patients with prolonged myelosuppression or repeated episodes of myelosuppression to assess leukemia status and marrow cellularity. Evaluate thiopurine S-methyltransferase (TPMT) and nucleotide diphosphatase (NUDT15) status in patients with severe myelosuppression or repeated episodes of myelosuppression [see Dosage and Administration ( 2.2 )] . If a patient misses a dose, instruct the patient to continue with the next scheduled dose. 2.2 Dosage Modifications in Patients with TPMT and NUDT15 Deficiency Consider testing for TPMT and NUDT15 deficiency in patients who experience severe myelosuppression or repeated episodes of myelosuppression [see Warnings and Precautions ( 5.1 ), Clinical Pharmacology ( 12.5 )] . Homozygous Deficiency in either TPMT or NUDT15 Patients with homozygous deficiency of either enzyme typically require 10% or less of the recommended dosage. Reduce the recommended starting dosage of mercaptopurine in patients who are known to have homozygous TPMT or NUDT15 deficiency. Heterozygous Deficiency in TPMT and/or NUDT15 Reduce the mercaptopurine dosage based on tolerability. Most patients with heterozygous TPMT or NUDT15 deficiency tolerate recommended dosage, but some require dose reduction based on adverse reactions. Patients who are heterozygous for both TPMT and NUDT15 may require more substantial dose reductions. 2.3 Dosage Modifications in Renal and Hepatic Impairment Renal Impairment Use the lowest recommended starting dosage for mercaptopurine in patients with renal impairment (CLcr less than 50 mL/min). Adjust the dosage to maintain absolute neutrophil count (ANC) at a desirable level and for adverse reactions [see Uses in Specific Populations ( 8.6 )] . Hepatic Impairment Use the lowest recommended starting dosage for mercaptopurine in patients with hepatic impairment. Adjust the dosage to maintain absolute neutrophil count (ANC) at a desirable level and for adverse reactions [see Uses in Specific Populations ( 8.7 )] . 2.4 Dosage Modification with Concomitant Use of Allopurinol Reduce the dose of mercaptopurine to one-third to one-quarter of the current dosage when coadministered with allopurinol [see Drug Interactions ( 7.1 )] . 2.5 Administration Shake the bottle vigorously for at least 30 seconds to ensure the oral suspension is well mixed. Mercaptopurine oral suspension is a pink to brown viscous oral suspension. Provide a press-in bottle adapter and two oral dispensing syringes (one 1 mL and one 5 mL). Train patients or caregivers on proper handling, storage, administration, disposal and clean-up of accidental spillage prior to initiation of mercaptopurine oral suspension and during each visit to the clinic. Advise patients and caregivers to use mercaptopurine oral suspension within 8 weeks and properly discard remaining mercaptopurine oral suspension after 8 weeks. Provide instructions regarding which syringe to use and how to administer the specified dose, since mercaptopurine oral sus

6 ADVERSE REACTIONS The following clinically significant adverse reactions are described elsewhere in the labeling: • Myelosuppression [see Warnings and Precautions ( 5.1 )] • Hepatotoxicity [see Warnings and Precautions ( 5.2 )] • Immunosuppression [see Warnings and Precautions ( 5.3 )] • Treatment Related Malignancies [see Warnings and Precautions ( 5.4 )] • Macrophage Activation Syndrome [see Warnings and Precautions ( 5.5 )] The most common adverse reaction (>20%) is myelosuppression, including anemia, neutropenia, lymphopenia and thrombocytopenia. Adverse reactions occurring in 5% to 20% of patients include anorexia, nausea, vomiting, diarrhea, malaise and rash. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Hikma Pharmaceuticals USA Inc. at 1-800-962-8364 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. Based on multicenter cooperative group ALL trials, the most common adverse reaction occurring in > 20% of patients was myelosuppression, including anemia, neutropenia, lymphopenia and thrombocytopenia. Adverse reactions occurring in 5% to 20% of patients included anorexia, nausea, vomiting, diarrhea, malaise, and rash. Adverse reactions occurring in < 5% of patients included urticaria, hyperuricemia, oral lesions, elevated transaminases, hyperbilirubinemia, hyperpigmentation, infections, and pancreatitis. Oral lesions resemble thrush rather than antifolic ulcerations. Delayed or late toxicities include hepatic fibrosis, hyperbilirubinemia, alopecia, pulmonary fibrosis, oligospermia and secondary malignancies [see Warnings and Precautions ( 5.1 , 5.2 )] . Drug fever has been reported with mercaptopurine. 6.2 Postmarketing Experience The following adverse reactions have been identified during postapproval use of mercaptopurine. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure. These reactions include: photosensitivity, hypoglycemia, portal hypertension, intrahepatic cholestasis of pregnancy (ICP), pellagra, and erythema nodosum.

5 WARNINGS AND PRECAUTIONS • Myelosuppression : Monitor complete blood count (CBC) and adjust the dose of mercaptopurine for excessive myelosuppression. Consider testing in patients with severe myelosuppression or repeated episodes of myelosuppression for thiopurine S-methyltransferase (TPMT) or nucleotide diphosphatase (NUDT15) deficiency. Patients with homozygous-TPMT or homozygous-NUDT15 deficiency may require a dose reduction. ( 2.2 , 5.1 ) • Hepatotoxicity : Monitor transaminases, alkaline phosphatase and bilirubin. Withhold mercaptopurine at onset of hepatotoxicity. ( 5.2 ) • Immunosuppression : Response to all vaccines may be diminished and there is a risk of infection with live virus vaccines. Consult immunization guidelines for immunocompromised pediatrics. ( 5.3 ) • Treatment Related Malignancies : Aggressive and fatal cases of hepatosplenic T-cell lymphoma have occurred. ( 5.4 ) • Macrophage Activation Syndrome : Monitor for and treat promptly; discontinue mercaptopurine. ( 5.5 ) • Embryo-Fetal Toxicity : Can cause fetal harm. Advise patients of reproductive potential of the potential risk to a fetus and to use effective contraception. ( 5.6 , 8.1 , 8.3 ) • Phenylketonuria : Patients should be informed that mercaptopurine oral suspension contains phenylalanine, a component of aspartame. Each mL of the 20 mg/mL oral suspension contains 0.015 mg of phenylalanine. ( 5.7 ) 5.1 Myelosuppression The most consistent, dose-related adverse reaction of mercaptopurine is myelosuppression, manifested by anemia, leukopenia, thrombocytopenia, or any combination of these. Monitor CBC and adjust the dosage of mercaptopurine for excessive myelosuppression [see Dosage and Administration ( 2.1 )] . Consider testing for thiopurine S-methyltransferase (TPMT) or nucleotide diphosphatase (NUDT15) deficiency in patients with severe myelosuppression or repeated episodes of myelosuppression. TPMT genotyping or phenotyping (red blood cell TPMT activity) and NUDT15 genotyping can identify patients who have reduced activity of these enzymes. Patients with homozygous TPMT or NUDT15 deficiency may require a dose reduction [see Dosage and Administration ( 2.2 ), Clinical Pharmacology ( 12.5 )] . Myelosuppression can be exacerbated by coadministration with allopurinol, aminosalicylates or other products that cause myelosuppression [see Drug Interactions ( 7.1 , 7.3 , 7.4 )] . Reduce the dosage of mercaptopurine when coadministered with allopurinol [see Dosage and Administration ( 2.4 )] . 5.2 Hepatotoxicity Mercaptopurine is hepatotoxic. There are reports of deaths attributed to hepatic necrosis associated with the administration of mercaptopurine. Hepatic injury can occur with any dosage but seems to occur with greater frequency when the recommended dosage is exceeded. In some patients, jaundice has cleared following withdrawal of mercaptopurine and reappeared with rechallenge. Usually, clinically detectable jaundice appears early in the course of treatment (1 to 2 months); however, jaundice has been reported as early as 1 week and as late as 8 years after starting mercaptopurine. The hepatotoxicity has been associated in some cases with anorexia, diarrhea, jaundice, ascites, and pruritus. Hepatic encephalopathy has occurred. Monitor serum transaminase levels, alkaline phosphatase, and bilirubin levels at weekly intervals when first beginning therapy and at monthly intervals thereafter. Monitor liver tests more frequently in patients who are receiving mercaptopurine with other hepatotoxic drugs [see Drug Interactions ( 7.5 )] or with known pre-existing liver disease. Withhold mercaptopurine at onset of hepatotoxicity. Intrahepatic Cholestasis of Pregnancy Postmarketing cases of intrahepatic cholestasis of pregnancy (ICP) have been reported in patients with inflammatory bowel disease who received mercaptopurine during pregnancy. Mercaptopurine is not indicated for use in inflammatory bowel disease [see Indications and Usage ( 1.1 )] . Discontinue m

4 CONTRAINDICATIONS None. • None

10 OVERDOSAGE Signs and symptoms of mercaptopurine overdosage may be immediate (anorexia, nausea, vomiting, and diarrhea) or delayed (myelosuppression, liver dysfunction, and gastroenteritis). Dialysis cannot be expected to clear mercaptopurine. Hemodialysis is thought to be of marginal use due to the rapid intracellular incorporation of mercaptopurine into active metabolites with long persistence. Withhold mercaptopurine immediately if severe or life-threatening adverse reactions occur during treatment. If a patient is seen immediately following an accidental overdosage, it may be useful to induce emesis.