MERCAPTOPURINE- mercaptopurine_tablet

Animal Data
Mercaptopurine was embryo-lethal and teratogenic in several animal species (rat, mouse, rabbit, and hamster) at doses less than the recommended human dose.
CLINICAL PHARMACOLOGY
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. Mercaptopurine exposure-response relationships and the time course of pharmacodynamics response are unknown. Following a single oral dose of mercaptopurine 50 mg under fasted conditions to adult healthy subjects, the mean AUC 0-INF max Food has been shown to decrease the exposure of mercaptopurine. The volume of distribution usually exceeded that of the total body water. There is negligible entry of mercaptopurine into cerebrospinal fluid. Plasma protein binding averages 19% over the concentration range 10 to 50 mcg/mL (a concentration only achieved by intravenous administration of mercaptopurine at doses exceeding 5 to 10 mg/kg). The elimination half-life is less than 2 hours following a single oral dose. Mercaptopurine is inactivated via two major pathways. One is thiol methylation, which is catalyzed by the polymorphic enzyme thiopurine S-methyltransferase (TPMT), to form the inactive metabolite methyl-mercaptopurine. The second inactivation pathway is oxidation, which is catalyzed by xanthine oxidase. The product of oxidation is the inactive metabolite 6-thiouric acid. Following the oral administration of radiolabeled mercaptopurine, 46% of the dose was recovered in the urine (as parent drug and metabolites) in the first 24 hours. Several published studies indicate that patients with reduced TPMT or NUDT15 activity receiving usual doses of mercaptopurine, accumulate excessive cellular concentrations of active 6-TGNs, and are at higher risk for severe myelosuppression. In a study of 1028 children with ALL, the approximate tolerated mercaptopurine dosage for patients with TPMT and/or NUDT15 deficiency on mercaptopurine maintenance therapy (as a percentage of the planned dosage) was as follows: heterozygous for either TPMT or NUDT15, 50-90%; heterozygous for both TPMT and NUDT15, 30-50%; homozygous for either TPMT or NUDT15, 5-10%. Approximately 0. 3% (1:300) of patients of European or African ancestry have two loss-of-function alleles of the TPMT gene and have little or no TPMT activity (homozygous deficient or poor metabolizers), and approximately 10% of patients have one loss-of-function TPMT allele leading to intermediate TPMT activity (heterozygous deficient or intermediate metabolizers). The TPMT * * * NUDT15 deficiency is detected in < 1% of patients of European or African ancestry. Among patients of East Asian ancestry (i. , Chinese, Japanese, Vietnamese), 2% have two loss-of-function alleles of the NUDT15 gene, and approximately 21% have one loss-of-function allele. R139C variant of NUDT15 (present on the * * Consider all clinical information when interpreting results from phenotypic testing used to determine the level of thiopurine nucleotides or TPMT activity in erythrocytes, since some coadministered drugs can influence measurement of TPMT activity in blood and blood from recent transfusions will misrepresent a patient’s actual TPMT activity [see Dosage and Administration (2. 2) Warnings and Precautions (5.
Metabolism
Mercaptopurine is inactivated via two major pathways. One is thiol methylation, which is catalyzed by the polymorphic enzyme thiopurine S-methyltransferase (TPMT), to form the inactive metabolite methyl-mercaptopurine. The second inactivation pathway is oxidation, which is catalyzed by xanthine oxidase. The product of oxidation is the inactive metabolite 6-thiouric acid.
Excretion
Following the oral administration of radiolabeled mercaptopurine, 46% of the dose was recovered in the urine (as parent drug and metabolites) in the first 24 hours.

Mercaptopurine tablets are a nucleoside metabolic inhibitor indicated for treatment of adult and pediatric patients with acute lymphoblastic leukemia (ALL) as part of a combination chemotherapy maintenance regimen. 1 Mercaptopurine tablets are indicated for treatment of adult and pediatric patients with acute lymphoblastic leukemia (ALL) as part of a combination chemotherapy maintenance regimen.

1 Renal Impairment 2. 6 Hepatic Impairment 2. 7 The recommended starting dosage of mercaptopurine tablets is 1. 5 mg/kg to 2. 5 mg/kg orally once daily as part of combination chemotherapy maintenance regimen. A recommended dosage for patients less than 17 kg is not achievable, because the only available strength is 50 mg. Take mercaptopurine tablets either consistently with or without food. After initiating mercaptopurine tablets, monitor complete blood count (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 or myelosuppression [see Dosage and Administration (2. 2) Do not administer to patients who are unable to swallow tablets. If a patient misses a dose, instruct the patient to continue with the next scheduled dose. Mercaptopurine tablets are a cytotoxic drug. Follow special handling and disposal procedures. 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) Patients with homozygous deficiency of either enzyme typically require 10% or less of the recommended dosage. Reduce the recommended starting dosage of mercaptopurine tablets in patients who are known to have homozygous TPMT or NUDT15 deficiency. Reduce the mercaptopurine tablets dose based on tolerability. Most patients with heterozygous TPMT or NUDT15 deficiency tolerate the recommended dosage, but some require a dose reduction based on adverse reactions. Patients who are heterozygous for both TPMT and NUDT15 may require more substantial dose reductions. Use the lowest recommended starting dosage for mercaptopurine tablets 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) Use the lowest recommended starting dosage for mercaptopurine tablets in patients with hepatic impairment. 7) Reduce the dose of mercaptopurine tablets to one-third to one-quarter of the current dosage when coadministered with allopurinol [see Drug Interactions (7.

The following clinically significant adverse reactions are described elsewhere in the labeling: [see Warnings and Precautions (5. 1) [see Warnings and Precautions (5. 2) [see Warnings and Precautions (5. 3) [see Warnings and Precautions (5. 4) [see Warnings and Precautions (5. 5) The most common adverse reaction (> 20%) is myelosuppression, including anemia, leukopenia and thrombocytopenia. Adverse reactions occurring in 5% to 20% of patients include anorexia, nausea, vomiting, diarrhea, malaise and rash. 1 To report SUSPECTED ADVERSE REACTIONS, contact Mylan at 1-877-446-3679 (1-877-4-INFO-RX) or FDA at 1-800-FDA-1088 or www. gov/medwatch. 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, increased transaminases, hyperbilirubinemia, hyperpigmentation, infections, and pancreatitis. Oral lesions resemble thrush rather than antifolic ulcerations. Delayed or late adverse reactions include hepatic fibrosis, hyperbilirubinemia, alopecia, pulmonary fibrosis, oligospermia and secondary malignancies [see Warnings and Precautions (5. 2) Drug fever has been reported with mercaptopurine. Additional adverse reactions that have been reported in patients who have received mercaptopurine include photosensitivity, hypoglycemia, and portal hypertension. The following adverse reactions have been identified during postapproval use of mercaptopurine tablets. 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: intrahepatic cholestasis of pregnancy (ICP).

USE IN SPECIFIC POPULATIONS
Lactation 8. 2 Infertility 8. 3 Mercaptopurine tablets can cause fetal harm when administered to a pregnant woman [see Clinical Pharmacology (12. 1) (see Data The estimated background risk of major birth defects and miscarriage for the indicated population(s) is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively. Women receiving mercaptopurine in the first trimester of pregnancy have an increased incidence of miscarriage; the risk of malformation in offspring surviving first trimester exposure is not known. In a series of 28 women receiving mercaptopurine after the first trimester of pregnancy, 3 mothers died prior to delivery, 1 delivered a stillborn child, and 1 aborted; there were no cases of macroscopically abnormal fetuses. Mercaptopurine was embryo-lethal and teratogenic in several animal species (rat, mouse, rabbit, and hamster) at doses less than the recommended human dose. There are no data on the presence of mercaptopurine or its metabolites in human milk, the effects on the breastfed child, or the effects on milk production. Because of the potential for serious adverse reactions in the breastfed child, advise women not to breastfeed during treatment with mercaptopurine tablets and for 1 week after the last dose. Mercaptopurine tablets can cause fetal harm when administered to pregnant women [see Use in Specific Populations (8. 1) Verify the pregnancy status in females of reproductive potential prior to initiating mercaptopurine tablets [see Use in Specific Populations (8. 1) Advise females of reproductive potential to use effective contraception during treatment with mercaptopurine tablets and for 6 months after the last dose. Based on genotoxicity findings, advise males with female partners of reproductive potential to use effective contraception during treatment with mercaptopurine tablets and for 3 months after the last dose [see Nonclinical Toxicology (13. 1) Based on findings from animal studies, mercaptopurine tablets can impair female and male fertility [see Nonclinical Toxicology (13. 1) Safety and effectiveness of mercaptopurine tablets have been established in pediatric patients. Use of mercaptopurine tablets in pediatrics is supported by evidence from the published literature and clinical experience. Symptomatic hypoglycemia has been reported in pediatric patients with ALL receiving mercaptopurine. Reported cases were in pediatrics less than 6 years of age or with a low body mass index. Clinical studies of mercaptopurine did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or another drug therapy. Use the lowest recommended starting dosage for mercaptopurine tablets or increase the dosing interval to every 36-48 hours in patients with renal impairment (CLcr less than 50 mL/min). Adjust the dose to maintain absolute neutrophil count (ANC) at a desirable level and for adverse reactions [see Dosage and Administration (2. 3) Use the lowest recommended starting dosage for mercaptopurine tablets in patients with hepatic impairment.
Females
Advise females of reproductive potential to use effective contraception during treatment with mercaptopurine tablets and for 6 months after the last dose.
Males
Based on genotoxicity findings, advise males with female partners of reproductive potential to use effective contraception during treatment with mercaptopurine tablets and for 3 months after the last dose [see Nonclinical Toxicology (13.1)
Females and Males
Based on findings from animal studies, mercaptopurine tablets can impair female and male fertility [see Nonclinical Toxicology (13.1)

Allopurinol 2. 1 Warfarin 7. 2 Allopurinol can inhibit the first-pass oxidative metabolism of mercaptopurine by xanthine oxidase, which can lead to an increased risk of mercaptopurine adverse reactions (i. , myelosuppression, nausea, and vomiting) [see Warnings and Precautions (5. 1) Adverse Reactions (6. 1) [see Dosage and Administration (2. 4) The concomitant administration of mercaptopurine tablets and warfarin may decrease the anticoagulant effectiveness of warfarin. Monitor the international normalized ratio (INR) in patients receiving warfarin and adjust the warfarin dosage as appropriate. Mercaptopurine tablets can cause myelosuppression. Myelosuppression may be increased when mercaptopurine tablets are coadministered with other products that cause myelosuppression. Enhanced myelosuppression has been noted in some patients also receiving trimethoprim-sulfamethoxazole. Monitor the CBC and adjust the dose of mercaptopurine tablets for excessive myelosuppression [see Dosage and Administration (2. 1) Warnings and Precautions (5. 1) Aminosalicylates (e. , mesalamine, olsalazine or sulfasalazine) may inhibit the TPMT enzyme, which may increase the risk of myelosuppression when coadministered with mercaptopurine tablets. When aminosalicylates and mercaptopurine tablets are coadministered, use the lowest possible doses for each drug and monitor more frequently for myelosuppression [see Warnings and Precautions (5. 1) Mercaptopurine tablets can cause hepatotoxicity. Hepatotoxicity may be increased when mercaptopurine tablets are coadministered with other products that cause hepatotoxicity. Monitor liver tests more frequently in patients who are receiving mercaptopurine tablets with other hepatotoxic products [see Warnings and Precautions (5.

Human Data
Women receiving mercaptopurine in the first trimester of pregnancy have an increased incidence of miscarriage; the risk of malformation in offspring surviving first trimester exposure is not known. In a series of 28 women receiving mercaptopurine after the first trimester of pregnancy, 3 mothers died prior to delivery, 1 delivered a stillborn child, and 1 aborted; there were no cases of macroscopically abnormal fetuses.
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 tablets immediately for 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.
NONCLINICAL TOXICOLOGY
Mercaptopurine is carcinogenic in animals. Mercaptopurine causes chromosomal aberrations in cells derived from animals and humans and induces dominant-lethal mutations in the germ cells of male mice. Mercaptopurine can impair fertility. In mice, surviving female offspring of mothers who received chronic low doses of mercaptopurine during pregnancy were found sterile, or if they became pregnant, had smaller litters and more dead fetuses as compared to control animals.
REFERENCES
1.

Mylan Pharmaceuticals Inc.

MERCAPTOPURINE- mercaptopurine_tablet Product manual source documgent