The FDA is alerting health care providers of the rare risk of intrahepatic cholestasis of pregnancy (ICP) associated with the use of thiopurines (azathioprine, mercaptopurine, and thioguanine). Thiopurines have a known risk of hepatotoxicity and are currently labeled for risk of fetal harm with use during pregnancy. Pregnant patients should stop using thiopurines if they develop ICP. Reported cases of ICP occurred among pregnant patients using azathioprine or mercaptopurine for inflammatory bowel disease (eg, Crohn disease, ulcerative colitis) or systemic lupus erythematosus.
The FDA is requiring updates to the prescribing information to include the following: postmarketing cases of ICP have been reported in women treated with thiopurines during pregnancy; ICP symptoms and elevated bile acid levels improved following azathioprine discontinuation; and pregnant individuals should discontinue use of thiopurines if they develop ICP.
Further information may be found at https://www.fda.gov/drugs/drug-safety-and-availability/fda-alerts-health-care-professionals-pregnancy-problems-associated-thiopurines
Note: Consider testing for thiopurine S-methyltransferase (TPMT) and nudix hydrolase 15 (nucleotide diphosphatase [NUDT15]) deficiency; patients with TPMT or NUDT15 deficiency are at increased risk for severe toxicity at conventional mercaptopurine doses and generally require dose reduction (see Dosage adjustment for TPMT and/or NUDT15 deficiency below) (Ref).
Acute lymphoblastic leukemia (ALL): Maintenance: Oral: 1.5 to 2.5 mg/kg once daily (50 to 75 mg/m2 once daily); continue based on blood counts or
Off-label ALL dosing (combination chemotherapy; refer to specific reference for combinations):
Early intensification (two 4-week courses): 60 mg/m2/day days 1 to 14 (Ref).
Interim maintenance (12-week course): 60 mg/m2/day days 1 to 70 (Ref).
Maintenance (prolonged): 50 mg 3 times/day for 2 years (Ref) or 60 mg/m2/day for 2 years from diagnosis (Ref).
AALL0232 (Ref): Patients ≤30 years:
Consolidation: Oral: 60 mg/m2 once daily on days 1 to 14 and 29 to 42 of a 56-day cycle (in combination with cyclophosphamide, cytarabine, vincristine, pegaspargase, and intrathecal methotrexate).
Interim Maintenance 1 and 2: Oral: 25 mg/m2 once daily on days 1 to 56 (in combination with vincristine, high-dose methotrexate, and intrathecal methotrexate).
Maintenance phase: Oral: 75 mg/m2 once daily on days 1 to 84 of an 84-day cycle (in combination with vincristine, steroid, oral methotrexate, and intrathecal methotrexate). Maintenance cycles are repeated for a total duration of 2 years (females) and 3 years (males) from the start of Interim Maintenance I. During Maintenance, the mercaptopurine (and oral methotrexate) dose may be titrated to target absolute neutrophil count (ANC) and platelet count goals.
Acute promyelocytic leukemia, maintenance (off-label use): 60 mg/m2/day for 1 year (in combination with tretinoin and methotrexate) (Ref).
Crohn disease (off-label use): Oral:
Maintenance of remission: 0.75 to 1.5 mg/kg/day in combination with an antitumor necrosis factor agent (eg, adalimumab, infliximab) (Ref).
Management after surgical resection: 1.5 mg/kg/day (in combination with metronidazole) for ~18 months after surgery (Ref) or 50 mg once daily for 24 months, beginning prior to discharge from hospital (Ref).
Hepatitis, autoimmune (off-label use): Note: Reserve for patients with nonresponse or intolerance to first-line treatment. Oral: Initial: 25 mg once daily (in combination with a corticosteroid); may increase to 50 mg once daily as tolerated (Ref).
Lymphoblastic lymphoma (off-label use): Maintenance (prolonged): 50 mg 3 times daily for 2 years (Ref).
Ulcerative colitis, remission maintenance (off-label use): Oral: 1 to 1.5 mg/kg/day (Ref).
Dosage adjustment for TPMT and/or NUDT15 deficiency:
Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines (Ref):
Normal TPMT or NUDT15 activity (wild type): No initial dosage adjustment necessary; adjust dose based on condition being treated. Allow at least 2 weeks after each dosage adjustment to reach steady state. For patients receiving combination therapy, dosage adjustments (of all agents) should be made without any emphasis on mercaptopurine compared to other agents.
TPMT intermediate or possible intermediate metabolizer or NUDT15 intermediate or possible intermediate metabolizer : Initiate mercaptopurine with the dose reduced to 30% to 80% of the usual dose and adjust dose based on the degree of myelosuppression and condition being treated. Allow 2 to 4 weeks after each dosage adjustment to reach steady state. If myelosuppression occurs, the focus should be on reducing the mercaptopurine dose over other agents (depending on concomitant therapy). If the starting dose is already below the normal recommended dose, dose reduction may not be recommended.
TPMT poor metabolizer: When used for malignancy, initiate mercaptopurine at a drastically reduced dose (reduce the daily dose by 10-fold and reduce the frequency from once daily to 3 times a week). Adjust dose based on the degree of myelosuppression and condition being treated. Allow 4 to 6 weeks after each dosage adjustment to reach steady state. If myelosuppression occurs, the focus should be on reducing the mercaptopurine dose over other agents (depending on concomitant therapy). When used for nonmalignant conditions, consider alternative (non-thiopurine) immunosuppressant therapy.
NUDT15 poor metabolizer: When used for malignancy, initiate mercaptopurine at 10 mg/m2/day. Adjust dose based on the degree of myelosuppression and condition being treated. Allow 4 to 6 weeks after each dosage adjustment to reach steady state. If myelosuppression occurs, the focus should be on reducing the mercaptopurine dose over other agents (depending on concomitant therapy). When used for nonmalignant conditions, consider alternative (non-thiopurine) immunosuppressant therapy.
Manufacturer’s labeling:
Heterozygous deficiency (intermediate activity): Reduce the dose based on tolerability; most patients with heterozygous deficiency of TPMT or NUDT15 tolerate recommended doses, although some require dosage reduction. Patients who are heterozygous for both TPMT and NUDT15 may require more substantial dose reductions.
Homozygous deficiency (low or deficient activity): Reduce the mercaptopurine dose to 10% of the usual dose or lower for homozygous deficiency in either TPMT or NUDT15.
Missed dose: If a dose is missed, continue with the next scheduled dose.
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
CrCl ≥50 mL/minute: There are no dosage adjustments provided in the manufacturer's labeling.
CrCl <50 mL/minute: Initiate with the lowest recommended starting dose or increase the dosing interval to every 36 to 48 hours to avoid accumulation in patients with renal impairment adjust dose to maintain desirable ANC level and for adverse reactions.
Hepatic impairment at baseline: Initiate with the lowest recommended starting dose; adjust dose to maintain desirable ANC level and for adverse reactions.
Hepatotoxicity during treatment: Withhold mercaptopurine therapy.
Intrahepatic cholestasis of pregnancy during treatment: Discontinue mercaptopurine therapy.
American Society of Clinical Oncology guidelines for appropriate systemic therapy dosing in adults with cancer with a BMI ≥30 kg/m2: Utilize patient's actual body weight for calculation of BSA- or weight-based dosing; manage regimen-related toxicities in the same manner as for patients with a BMI <30 kg/m2; if a dose reduction is utilized due to toxicity, may consider resumption of full, weight-based dosing (or previously tolerated dose level) with subsequent cycles only if dose escalations are allowed in the prescribing information, if contributing underlying factors (eg, hepatic or kidney impairment) are sufficiently resolved, AND if performance status has markedly improved or is considered adequate (Ref).
Adjust dosage for excessive hematologic toxicity.
Due to renal decline with age, initiate treatment at the low end of recommended dose range.
(For additional information see "Mercaptopurine: Pediatric drug information")
Dosage guidance:
Safety: Consider testing for thiopurine S-methyltransferase (TPMT) and nudix hydrolase 15 (nucleotide diphosphatase [NUDT15]) deficiency, patients with minimal or no TPMT activity are at increased risk for severe toxicity at conventional mercaptopurine doses and generally require dose reduction (see "Dosage Adjustment for TPMT or NUDT15 Deficiency" below). Pediatric doses presented as mg/m2 and mg/kg; use caution.
Acute lymphoblastic leukemia (ALL): Limited data available; multiple regimens/protocols reported; refer to specific protocols.
Standard risk (Ref): Children 1 to <10 years: Consolidation, Interim Maintenance I and Maintenance: Oral: 75 mg/m2 once daily, frequency and duration dependent on protocol phase (in combination with vincristine, steroid, and methotrexate [oral and/or intrathecal]). Maintenance cycles are repeated for a total duration of 2 years (females) and 3 years (males) from the start of Interim Maintenance I. During Maintenance, oral methotrexate and mercaptopurine are adjusted to maintain a target ANC goal (generally 1,000 to 2,000/mm3; varies based on protocol).
High risk (Ref):
Children and Adolescents:
Consolidation: Oral: 60 mg/m2 once daily on days 1 to 14 and 29 to 42 of a 56-day cycle (in combination with cyclophosphamide, cytarabine, vincristine, pegaspargase, and intrathecal methotrexate).
Interim Maintenance 1 and 2: Oral: 25 mg/m2 once daily on days 1 to 56 (in combination with vincristine, high-dose methotrexate, and intrathecal methotrexate).
Maintenance phase: Oral: 75 mg/m2 once daily on days 1 to 84 of an 84-day cycle (in combination with vincristine, steroid, oral methotrexate, and intrathecal methotrexate). Maintenance cycles duration: 2 to 3 years (refer to specific protocol). During Maintenance, the oral methotrexate and mercaptopurine are titrated to a target ANC goal (generally 1,000 to 2,000/mm3; varies based on protocol).
Acute promyelocytic leukemia (APL): Limited data available; multiple regimens reported:
Combination with tretinoin: Maintenance phase: Children and Adolescents ≤14 years: Oral: 100 mg/m2/day for 14 days of a 28-day cycle in combination with tretinoin. Cycles were repeated every 28 days for 2 years (Ref).
Combination with tretinoin and methotrexate:
Kutny 2017: AAML0631: Maintenance phase: Children ≥2 years and Adolescents: Oral: 50 mg/m2/day for 9 cycles of 12 weeks in combination with methotrexate and tretinoin.
Ortega 2005: PETHEMA Group: Maintenance phase: Children and Adolescents <17 years: Oral: 50 mg/m2/day for 2 years in combination with methotrexate and tretinoin. Doses of mercaptopurine and methotrexate were decreased by 50% if the WBC count was <3,500 cells/mm3 and discontinued for WBC <2,500/mm3.
Powell 2010: North American Leukemia Intergroup Study C9710: Maintenance phase: Adolescents ≥15 years: Oral: 60 mg/m2/day for 1 year in combination with tretinoin and methotrexate.
Crohn disease, remission maintenance: Limited data available: Children and Adolescents: Oral: 1 to 1.5 mg/kg/day (Ref).
Hepatitis, autoimmune (alternative agent): Limited data available: Note: Use should be reserved for patients not responsive or intolerant of other therapies (Ref).
Children and Adolescents: Oral: Initial: 0.5 to 1 mg/kg/day; monitor serum levels and adjust dose accordingly; a higher dose of 1.5 mg/kg/day has also been suggested (Ref).
Ulcerative colitis, remission maintenance: Limited data available: Children and Adolescents: Oral: 1 to 1.5 mg/kg/day (Ref).
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
Dosing adjustment in TPMT and/or NUDT15 deficiency: Limited data available:
Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines (Ref):
Normal TPMT or NUDT15 activity (wild type): No initial dosage adjustment necessary; adjust dose based on condition being treated. Allow at least 2 weeks after each dosage adjustment to reach steady state. For patients receiving combination therapy, dosage adjustments (of all agents) should be made without any emphasis on mercaptopurine compared to other agents.
TPMT intermediate or possible intermediate metabolizer or NUDT15 intermediate or possible intermediate metabolizer: Initiate mercaptopurine with the dose reduced to 30% to 80% of the usual dose and adjust dose based on the degree of myelosuppression and condition being treated. Allow 2 to 4 weeks after each dosage adjustment to reach steady state. If myelosuppression occurs, the focus should be on reducing the mercaptopurine dose over other agents (depending on concomitant therapy). If the starting dose is already below the normal recommended dose, dose reduction may not be recommended.
TPMT poor metabolizer:
• When used for malignancy, initiate mercaptopurine at a drastically reduced dose (reduce the daily dose by 10-fold and reduce the frequency from once daily to 3 times a week). Adjust dose based on the degree of myelosuppression and condition being treated. Allow 4 to 6 weeks after each dosage adjustment to reach steady state. If myelosuppression occurs, the focus should be on reducing the mercaptopurine dose over other agents (depending on concomitant therapy).
• When used for nonmalignant conditions, consider alternative (non-thiopurine) immunosuppressant therapy.
NUDT15 poor metabolizer:
• When used for malignancy, initiate mercaptopurine at 10 mg/m2/day. Adjust dose based on the degree of myelosuppression and condition being treated. Allow 4 to 6 weeks after each dosage adjustment to reach steady state. If myelosuppression occurs, the focus should be on reducing the mercaptopurine dose over other agents (depending on concomitant therapy).
• When used for nonmalignant conditions, consider alternative (non-thiopurine) immunosuppressant therapy.
Manufacturer's labeling:
Heterozygous deficiency (intermediate activity): Reduce the dose based on tolerability; most patients with heterozygous deficiency of TPMT or NUDT15 tolerate recommended doses, although some require dosage reduction. Patients who are heterozygous for both TPMT and NUDT15 may require more substantial dose reductions.
Homozygous deficiency (low or deficient activity): Reduce the mercaptopurine dose to 10% of the usual dose or lower for homozygous deficiency in either TPMT or NUDT15.
Children and Adolescents:
CrCl ≥50 mL/minute: No adjustment required (Ref).
CrCl <50 mL/minute: Initiate with the lowest recommended starting dose or increase the dosing interval to every 36 to 48 hours to avoid accumulation in patients with renal impairment adjust dose to maintain desirable ANC level and for adverse reactions (Ref).
Hemodialysis: Administer every 48 hours (Ref).
Continuous ambulatory peritoneal dialysis (CAPD): Administer every 48 hours (Ref).
Continuous renal replacement therapy (CRRT): Administer every 48 hours (Ref).
Children and Adolescents:
Hepatic impairment at baseline: Initiate with the lowest recommended starting dose; adjust dose to maintain desirable ANC level and for adverse reactions.
Hepatotoxicity during treatment: Withhold therapy.
The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.
>10%:
Dermatologic: Skin rash (5% to 20%)
Gastrointestinal: Anorexia (5% to 20%), diarrhea (5% to 20%), nausea (5% to 20%), vomiting (5% to 20%)
Hematologic & oncologic: Bone marrow depression (dose-related: >20%; including anemia, lymphocytopenia, neutropenia, thrombocytopenia)
Nervous system: Malaise (5% to 20%)
1% to 10%:
Dermatologic: Hyperpigmentation (<5%), urticaria (<5%)
Endocrine & metabolic: Hyperuricemia (<5%)
Gastrointestinal: Oral lesion (<5%), pancreatitis (<5%)
Hepatic: Hyperbilirubinemia (<5%), increased serum transaminases (<5%)
Infection: Infection (<5%)
Frequency not defined:
Dermatologic: Alopecia
Gastrointestinal: Cholestasis, sprue-like symptoms, ulcerative bowel lesion
Genitourinary: Oligospermia
Hematologic & oncologic: Granulocytopenia, leukopenia, metastases (secondary)
Hepatic: Ascites, hepatic encephalopathy, hepatic fibrosis, hepatic injury, hepatic necrosis, hepatomegaly, hepatotoxicity, intrahepatic cholestasis, jaundice, toxic hepatitis
Immunologic: Immunosuppression
Renal: Nephrotoxicity
Respiratory: Pulmonary fibrosis
Miscellaneous: Drug fever
Postmarketing:
Cardiovascular: Portal hypertension
Dermatologic: Skin photosensitivity
Endocrine & metabolic: Hypoglycemia
There are no contraindications listed in the US manufacturer's labeling.
Canadian labeling: Hypersensitivity to mercaptopurine or any component of the formulation; patients whose disease showed prior resistance to mercaptopurine; immunizations with live organism vaccines.
Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
Concerns related to adverse effects:
• Bone marrow suppression: Dose-related leukopenia, thrombocytopenia, and anemia are common; however, may also be indicative of disease progression. Hematologic toxicity may be delayed. Bone marrow may appear hypoplastic (could also appear normal). Monitor blood counts; dose may require modification for severe neutropenia or thrombocytopenia. Monitor for bleeding (due to thrombocytopenia) or infection (due to neutropenia). Profound severe or repeated hematologic toxicity may be indicative of thiopurine methyltransferase (TPMT) deficiency or nudix hydrolase 15 (nucleotide diphosphatase [NUDT15]) deficiency (see “TPMT or NUDT15 deficiency” below); patients who are homozygous for TPMT or NUDT15 deficiency may require substantial dosage reductions. TPMT genotyping or phenotyping or NUDT15 genotyping can identify patients with reduced TPMT or NUDT15 enzyme activity.
• Hepatotoxicity: Hepatotoxicity has been reported, including jaundice, ascites, pruritus, hepatic necrosis (may be fatal), intrahepatic cholestasis (including intrahepatic cholestasis of pregnancy), parenchymal cell necrosis, and/or hepatic encephalopathy; may be due to direct hepatic cell damage or hypersensitivity. While hepatotoxicity or hepatic injury may occur at any dose, dosages exceeding the recommended dose are associated with a higher incidence. Signs of jaundice generally appear early in treatment, after ~1 to 2 months (range: 1 week to 8 years) and may resolve following discontinuation; recurrence with rechallenge has been noted.
• Immunosuppression: Mercaptopurine is immunosuppressive; immune responses to infections may be impaired and the risk for infection is increased. Common signs of infection, such as fever and leukocytosis may not occur; lethargy and confusion may be more prominent signs of infection.
• Macrophage activation syndrome: Macrophage activation syndrome (MAS), also known as hemophagocytic lymphohistiocytosis, is a life-threatening disorder which may develop in patients with autoimmune disorders (particularly inflammatory bowel disease); mercaptopurine use for the treatment of autoimmune conditions (off-label use) may cause increased susceptibility to MAS. Discontinue mercaptopurine if MAS develops or is suspected. Monitor; promptly treat infections such as Epstein-Barr virus (EBV) and cytomegalovirus (which are known triggers for MAS).
• Photosensitivity: Minimize sun exposure due to possible photosensitivity.
• Secondary malignancy: Immunosuppressive agents, including mercaptopurine, are associated with the development of lymphoproliferative disorders and other malignancies. In an analysis of T-cell lymphomas associated with TNF blockers (with or without thiopurines) for the treatment of rheumatoid arthritis, Crohn disease, ulcerative colitis, or ankylosing spondylitis (off-label uses for thiopurines), an increase in the incidence of T-cell lymphomas, most commonly mycosis fungoides/Sézary syndrome and hepatosplenic T-cell lymphoma (HSTCL) was reported (Deepak 2013). HSTCL is a rare white blood cell cancer that is usually fatal. Most HSTCL cases occurred in patients treated with a combination of TNF blockers and thiopurines, although cases of HSTCL also occurred in patients receiving azathioprine or mercaptopurine monotherapy. Skin cancers (melanoma and non-melanoma), Kaposi and non-Kaposi sarcomas, and uterine cervical cancer in situ have been reported in patients receiving immunosuppressive treatment (including mercaptopurine); risk of development may be related to the degree and duration of immunosuppression. Partial regression of lymphoproliferative disorders may occur upon therapy discontinuation. Regimens containing multiple immunosuppressants increase the risk of EBV-associated lymphoproliferative disorders; use with caution.
Disease-related concerns:
• Renal impairment: Reduce initial dose or extend dosing interval in patients with renal impairment (CrCl <50 mL/minute). Some renal adverse effects may be minimized with hydration and prophylactic antihyperuricemic therapy.
• TPMT or NUDT15 deficiency: Patients with reduced TPMT or NUDT15 activity have a higher risk of severe myelosuppression with usual doses of thiopurines (eg, mercaptopurine, azathioprine, thioguanine) and may require substantial thiopurine dose reductions. Individuals who are TPMT homozygous or compound heterozygous deficient are at very high risk for severe myelosuppression (Relling 2019). TPMT genotyping or phenotyping and NUDT15 genotyping may assist in identifying patients at risk for developing toxicity. Consider testing for NUDT15 and TPMT deficiency in patients who experience severe bone marrow toxicities or repeated myelosuppressive episodes. Accurate phenotyping (red blood cell TPMT activity) results are not possible in patients who have received recent blood transfusions. The Clinical Pharmacogenetics Implementation Consortium (CPIC) guideline for thiopurine dosing based on TPMT and NUDT15 genotypes (Relling 2019) recommends reduced initial doses for TPMT and NUDT15 intermediate (and possible intermediate) metabolizers (with dosage adjustments based on myelosuppression). For TPMT and NUDT15 poor metabolizers, CPIC guideline recommends considering alternative nonthiopurine agents for nonmalignant conditions and drastically reduced doses if used to treat malignancy. Genetic TPMT deficiency is the primary cause of thiopurine intolerance in Europeans and Africans; NUDT15 risk alleles are associated with a majority of thiopurine intolerance in Asians and are also common in Hispanics (Relling 2019).
Special populations:
• Pediatric: Cases of symptomatic hypoglycemia have been reported in children receiving mercaptopurine for the treatment of ALL; cases were reported in children less than 6 years of age or with a low body mass index.
Other warnings/precautions:
• Error-prone terms: To avoid potentially serious dosage errors, the terms “6-mercaptopurine” or “6-MP” should be avoided; use of these terms has been associated with six-fold overdosages.
• Vaccines: Immune response to vaccines may be diminished. Live virus vaccines impose a risk for infection.
The development of secondary hemophagocytic lymphohistiocytosis (HLH), a rare and frequently fatal activation of macrophages which causes phagocytosis of all bone marrow blood cell lines, is increased (100-fold) in pediatric patients diagnosed with inflammatory bowel disease; this risk is further increased with concomitant thiopurine (ie, azathioprine, mercaptopurine) therapy, Epstein-Barr virus, or other possible infections; if patient presents with fever (at least 5 days), cervical lymphadenopathy, and lymphopenia, discontinue immunosuppressive therapy and further diagnostic evaluation for HLH should be performed; diagnostic delay associated with increased mortality (Biank 2011).
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Suspension, Oral:
Purixan: 2000 mg/100 mL (100 mL) [contains aspartame, methylparaben, propylparaben]
Tablet, Oral:
Generic: 50 mg
May be product dependent
Suspension (Purixan Oral)
2000 mg/100 mL (per mL): $17.19
Tablets (Mercaptopurine Oral)
50 mg (per each): $4.09 - $8.18
Disclaimer: A representative AWP (Average Wholesale Price) price or price range is provided as reference price only. A range is provided when more than one manufacturer's AWP price is available and uses the low and high price reported by the manufacturers to determine the range. The pricing data should be used for benchmarking purposes only, and as such should not be used alone to set or adjudicate any prices for reimbursement or purchasing functions or considered to be an exact price for a single product and/or manufacturer. Medi-Span expressly disclaims all warranties of any kind or nature, whether express or implied, and assumes no liability with respect to accuracy of price or price range data published in its solutions. In no event shall Medi-Span be liable for special, indirect, incidental, or consequential damages arising from use of price or price range data. Pricing data is updated monthly.
Excipient information presented when available (limited, particularly for generics); consult specific product labeling.
Tablet, Oral:
Purinethol: 50 mg
Generic: 50 mg
Oral: Administer at the same time(s) each day. Administer preferably on an empty stomach (Ref); avoid concomitant milk products if possible (Ref). The manufacturer recommends taking consistently either with or without food.
If adherence is limited by administering on an empty stomach in the evening or by avoiding concomitant milk products, simplification of administration (eg, take with food/dairy without regard to time of day) should be considered. In adherent patients (taking mercaptopurine regularly), no association was seen between risk of ALL relapse and mercaptopurine ingestion habits; there was also no association noted with red cell thioguanine nucleotide (TGN) levels and administration with food, dairy, or time of day (Ref).
Suspension: Shake vigorously for at least 30 seconds to ensure suspension is mixed thoroughly (suspension is viscous). Measure dose with an oral dosing syringe (a 1 mL and a 5 mL oral dosing syringe are supplied by the manufacturer) to assure proper dose is administered. Patients and caregivers should be trained on appropriate measuring and administration, handling, storage, disposal, cleanup of accidental spills, and proper cleaning of oral dosing syringe. Use within 8 weeks after opening.
Oral: Administer at the same time(s) each day, preferably on an empty stomach (Ref); avoid concomitant milk products if possible (Ref).
Acute lymphoblastic leukemia (ALL): Administration in the evening has demonstrated superior outcome; administration with food did not significantly affect outcome (Ref).
If adherence is limited by administering on an empty stomach in the evening or by avoiding concomitant milk products, simplification of administration (eg, take with food/dairy without regard to time of day) should be considered. In adherent patients (taking mercaptopurine regularly), no association was seen between risk of ALL relapse and mercaptopurine ingestion habits; there was also no association noted with red cell thioguanine nucleotide (TGN) levels and administration with food, dairy, or time of day (Ref).
Suspension: Shake well for at least 30 seconds to ensure suspension is mixed thoroughly (suspension is viscous). Measure dose with an oral dosing syringe (a 1 mL and a 5 mL oral dosing syringe are supplied by the manufacturer) to assure proper dose is administered. If oral syringe is intended to be re-used, wash with warm soapy water and rinse well (hold syringe under water and move plunger several times to ensure inside of syringe is clean); allow to dry completely. Patients and caregivers should be trained on appropriate measuring and administration, handling, storage, disposal, cleanup of accidental spills, and proper cleaning of oral dosing syringe. Use within 8 weeks after opening.
Hazardous agent (NIOSH 2016 [group 1]).
Use appropriate precautions for receiving, handling, storage, preparation, dispensing, transporting, administration, and disposal. Follow NIOSH and USP 800 recommendations and institution-specific policies/procedures for appropriate containment strategy (NIOSH 2016; USP-NF 2020).
Acute lymphoblastic leukemia: Treatment of acute lymphoblastic leukemia (ALL), as part of a combination chemotherapy maintenance regimen.
Acute promyelocytic leukemia, maintenance; Crohn disease; Hepatitis, autoimmune; Lymphoblastic lymphoma; Ulcerative colitis (remission induction); Ulcerative colitis (remission maintenance)
Mercaptopurine may be confused with methotrexate
Purinethol [DSC] may be confused with propylthiouracil
The Institute for Safe Medication Practices (ISMP) includes this medication among its list of drug classes (chemotherapeutic agent, parenteral and oral; immunosuppressant agent, parenteral and oral) which have a heightened risk of causing significant patient harm when used in error (High-Alert Medications in Acute Care, Community/Ambulatory Care, and Long-Term Care Settings).
Mercaptopurine may be confused with mercaptamine [multiple international markets]
To avoid potentially serious dosage errors, the terms “6-mercaptopurine” or “6-MP” should be avoided; use of these terms has been associated with sixfold overdosages.
Azathioprine is metabolized to mercaptopurine; concurrent use of these commercially-available products has resulted in profound myelosuppression.
None known.
Note: Interacting drugs may not be individually listed below if they are part of a group interaction (eg, individual drugs within “CYP3A4 Inducers [Strong]” are NOT listed). For a complete list of drug interactions by individual drug name and detailed management recommendations, use the drug interactions program by clicking on the “Launch drug interactions program” link above.
5-Aminosalicylic Acid Derivatives: May enhance the myelosuppressive effect of Thiopurine Analogs. 5-Aminosalicylic Acid Derivatives may increase serum concentrations of the active metabolite(s) of Thiopurine Analogs. Specifically, exposure to the active 6-thioguanine nucleotides (6-TGN) may be increased. Risk C: Monitor therapy
Abrocitinib: May enhance the immunosuppressive effect of Immunosuppressants (Cytotoxic Chemotherapy). Risk X: Avoid combination
Allopurinol: May increase the serum concentration of Mercaptopurine. Allopurinol may also promote formation of active thioguanine nucleotides. Management: Reduce the mercaptopurine dose to one third to one quarter of the usual dose if used with allopurinol, and monitor closely for systemic toxicity. Risk D: Consider therapy modification
Antithymocyte Globulin (Equine): Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Antithymocyte Globulin (Equine). Specifically, these effects may be unmasked if the dose of cytotoxic chemotherapy is reduced. Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Antithymocyte Globulin (Equine). Specifically, infections may occur with greater severity and/or atypical presentations. Risk C: Monitor therapy
Antithyroid Agents: Myelosuppressive Agents may enhance the neutropenic effect of Antithyroid Agents. Risk C: Monitor therapy
Anti-TNF Agents: May enhance the adverse/toxic effect of Thiopurine Analogs. Specifically, the risk for T-cell non-Hodgkin's lymphoma (including hepatosplenic T-cell lymphoma) may be increased. Risk C: Monitor therapy
AzaTHIOprine: May enhance the myelosuppressive effect of Mercaptopurine. Risk X: Avoid combination
Baricitinib: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Baricitinib. Risk X: Avoid combination
BCG Products: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of BCG Products. Specifically, the risk of vaccine-associated infection may be increased. Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of BCG Products. Risk X: Avoid combination
Brincidofovir: Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Brincidofovir. Risk C: Monitor therapy
Brivudine: May enhance the adverse/toxic effect of Immunosuppressants (Cytotoxic Chemotherapy). Risk X: Avoid combination
Chikungunya Vaccine (Live): Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Chikungunya Vaccine (Live). Specifically, the risk of vaccine-associated infection may be increased. Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Chikungunya Vaccine (Live). Risk X: Avoid combination
Chloramphenicol (Ophthalmic): May enhance the adverse/toxic effect of Myelosuppressive Agents. Risk C: Monitor therapy
Chloramphenicol (Systemic): Myelosuppressive Agents may enhance the myelosuppressive effect of Chloramphenicol (Systemic). Risk X: Avoid combination
Cladribine: Agents that Undergo Intracellular Phosphorylation may diminish the therapeutic effect of Cladribine. Risk X: Avoid combination
Cladribine: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Cladribine. Risk X: Avoid combination
CloZAPine: Myelosuppressive Agents may enhance the adverse/toxic effect of CloZAPine. Specifically, the risk for neutropenia may be increased. Risk C: Monitor therapy
Coccidioides immitis Skin Test: Immunosuppressants (Cytotoxic Chemotherapy) may diminish the diagnostic effect of Coccidioides immitis Skin Test. Management: Consider discontinuing cytotoxic chemotherapy several weeks prior to coccidioides immitis skin antigen testing to increase the likelihood of accurate diagnostic results. Risk D: Consider therapy modification
COVID-19 Vaccine (Adenovirus Vector): Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of COVID-19 Vaccine (Adenovirus Vector). Management: Administer a 2nd dose using an mRNA COVID-19 vaccine (at least 4 weeks after the primary vaccine dose) and a bivalent booster dose (at least 2 months after the additional mRNA dose or any other boosters). Risk D: Consider therapy modification
COVID-19 Vaccine (Inactivated Virus): Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of COVID-19 Vaccine (Inactivated Virus). Risk C: Monitor therapy
COVID-19 Vaccine (mRNA): Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of COVID-19 Vaccine (mRNA). Management: Give a 3-dose primary series for all patients aged 6 months and older taking immunosuppressive medications or therapies. Booster doses are recommended for certain age groups. See CDC guidance for details. Risk D: Consider therapy modification
COVID-19 Vaccine (Subunit): Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of COVID-19 Vaccine (Subunit). Risk C: Monitor therapy
COVID-19 Vaccine (Virus-like Particles): Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of COVID-19 Vaccine (Virus-like Particles). Risk C: Monitor therapy
Deferiprone: Myelosuppressive Agents may enhance the neutropenic effect of Deferiprone. Management: Avoid the concomitant use of deferiprone and myelosuppressive agents whenever possible. If this combination cannot be avoided, monitor the absolute neutrophil count more closely. Risk D: Consider therapy modification
Dengue Tetravalent Vaccine (Live): Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Dengue Tetravalent Vaccine (Live). Specifically, the risk of vaccine-associated infection may be increased. Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Dengue Tetravalent Vaccine (Live). Risk X: Avoid combination
Denosumab: May enhance the immunosuppressive effect of Immunosuppressants (Cytotoxic Chemotherapy). Management: Consider the risk of serious infections versus the potential benefits of coadministration of denosumab and cytotoxic chemotherapy. If combined, monitor patients for signs/symptoms of serious infections. Risk D: Consider therapy modification
Deucravacitinib: May enhance the immunosuppressive effect of Immunosuppressants (Cytotoxic Chemotherapy). Risk X: Avoid combination
DOXOrubicin (Conventional): May enhance the hepatotoxic effect of Mercaptopurine. Risk C: Monitor therapy
Etrasimod: May enhance the immunosuppressive effect of Immunosuppressants (Cytotoxic Chemotherapy). Risk X: Avoid combination
Febuxostat: May increase the serum concentration of Mercaptopurine. Risk X: Avoid combination
Fexinidazole: Myelosuppressive Agents may enhance the myelosuppressive effect of Fexinidazole. Risk X: Avoid combination
Filgotinib: May enhance the immunosuppressive effect of Immunosuppressants (Cytotoxic Chemotherapy). Risk X: Avoid combination
Inebilizumab: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Inebilizumab. Risk C: Monitor therapy
Influenza Virus Vaccines: Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Influenza Virus Vaccines. Management: Administer influenza vaccines at least 2 weeks prior to initiating chemotherapy if possible. If vaccination occurs less than 2 weeks prior to or during chemotherapy, revaccinate at least 3 months after therapy discontinued if immune competence restored. Risk D: Consider therapy modification
Leflunomide: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Leflunomide. Management: Increase the frequency of chronic monitoring of platelet, white blood cell count, and hemoglobin or hematocrit to monthly, instead of every 6 to 8 weeks, if leflunomide is coadministered with immunosuppressive agents, such as cytotoxic chemotherapy. Risk D: Consider therapy modification
Lenograstim: Antineoplastic Agents may diminish the therapeutic effect of Lenograstim. Management: Avoid the use of lenograstim 24 hours before until 24 hours after the completion of myelosuppressive cytotoxic chemotherapy. Risk D: Consider therapy modification
Linezolid: May enhance the myelosuppressive effect of Myelosuppressive Agents. Risk C: Monitor therapy
Lipegfilgrastim: Antineoplastic Agents may diminish the therapeutic effect of Lipegfilgrastim. Management: Avoid concomitant use of lipegfilgrastim and myelosuppressive cytotoxic chemotherapy. Lipegfilgrastim should be administered at least 24 hours after the completion of myelosuppressive cytotoxic chemotherapy. Risk D: Consider therapy modification
Methotrexate: May increase the serum concentration of Mercaptopurine. Conversely, intracellular concentrations of thioguanine nucleotides may be decreased with the combination. Risk C: Monitor therapy
Mumps- Rubella- or Varicella-Containing Live Vaccines: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Mumps- Rubella- or Varicella-Containing Live Vaccines. Specifically, the risk of vaccine-associated infection may be increased. Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Mumps- Rubella- or Varicella-Containing Live Vaccines. Risk X: Avoid combination
Nadofaragene Firadenovec: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Nadofaragene Firadenovec. Specifically, the risk of disseminated adenovirus infection may be increased. Risk X: Avoid combination
Natalizumab: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Natalizumab. Risk X: Avoid combination
Ocrelizumab: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Ocrelizumab. Risk C: Monitor therapy
Ofatumumab: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Ofatumumab. Risk C: Monitor therapy
Olaparib: Myelosuppressive Agents may enhance the myelosuppressive effect of Olaparib. Risk C: Monitor therapy
Palifermin: May enhance the adverse/toxic effect of Antineoplastic Agents. Specifically, the duration and severity of oral mucositis may be increased. Management: Do not administer palifermin within 24 hours before, during infusion of, or within 24 hours after administration of myelotoxic chemotherapy. Risk D: Consider therapy modification
Pidotimod: Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Pidotimod. Risk C: Monitor therapy
Pimecrolimus: May enhance the immunosuppressive effect of Immunosuppressants (Cytotoxic Chemotherapy). Risk X: Avoid combination
Pneumococcal Vaccines: Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Pneumococcal Vaccines. Risk C: Monitor therapy
Poliovirus Vaccine (Live/Trivalent/Oral): Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Poliovirus Vaccine (Live/Trivalent/Oral). Specifically, the risk of vaccine-associated infection may be increased. Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Poliovirus Vaccine (Live/Trivalent/Oral). Risk X: Avoid combination
Polymethylmethacrylate: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the potential for allergic or hypersensitivity reactions to Polymethylmethacrylate. Management: Use caution when considering use of bovine collagen-containing implants such as the polymethylmethacrylate-based Bellafill brand implant in patients who are receiving immunosuppressants. Consider use of additional skin tests prior to administration. Risk D: Consider therapy modification
Promazine: May enhance the myelosuppressive effect of Myelosuppressive Agents. Risk C: Monitor therapy
Rabies Vaccine: Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Rabies Vaccine. Management: Complete rabies vaccination at least 2 weeks before initiation of immunosuppressant therapy if possible. If combined, check for rabies antibody titers, and if vaccination is for post exposure prophylaxis, administer a 5th dose of the vaccine. Risk D: Consider therapy modification
Ritlecitinib: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Ritlecitinib. Risk X: Avoid combination
Ropeginterferon Alfa-2b: Myelosuppressive Agents may enhance the myelosuppressive effect of Ropeginterferon Alfa-2b. Management: Avoid coadministration of ropeginterferon alfa-2b and other myelosuppressive agents. If this combination cannot be avoided, monitor patients for excessive myelosuppressive effects. Risk D: Consider therapy modification
Ruxolitinib (Topical): Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Ruxolitinib (Topical). Risk X: Avoid combination
Sipuleucel-T: Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Sipuleucel-T. Management: Consider reducing the dose or discontinuing the use of immunosuppressants, such as cytotoxic chemotherapy, prior to initiating sipuleucel-T therapy. Risk D: Consider therapy modification
Sphingosine 1-Phosphate (S1P) Receptor Modulator: May enhance the immunosuppressive effect of Immunosuppressants (Cytotoxic Chemotherapy). Risk C: Monitor therapy
Sulfamethoxazole: May enhance the myelosuppressive effect of Mercaptopurine. Risk C: Monitor therapy
Tacrolimus (Topical): Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Tacrolimus (Topical). Risk X: Avoid combination
Talimogene Laherparepvec: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Talimogene Laherparepvec. Specifically, the risk of infection from the live, attenuated herpes simplex virus contained in talimogene laherparepvec may be increased. Risk X: Avoid combination
Tertomotide: Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Tertomotide. Risk X: Avoid combination
Tofacitinib: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Tofacitinib. Risk X: Avoid combination
Trimethoprim: May enhance the myelosuppressive effect of Mercaptopurine. Risk C: Monitor therapy
Typhoid Vaccine: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Typhoid Vaccine. Specifically, the risk of vaccine-associated infection may be increased. Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Typhoid Vaccine. Risk X: Avoid combination
Ublituximab: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Ublituximab. Risk C: Monitor therapy
Upadacitinib: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the immunosuppressive effect of Upadacitinib. Risk X: Avoid combination
Vaccines (Live): Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Vaccines (Live). Specifically, the risk of vaccine-associated infection may be increased. Vaccines (Live) may diminish the therapeutic effect of Immunosuppressants (Cytotoxic Chemotherapy). Risk X: Avoid combination
Vaccines (Non-Live/Inactivated/Non-Replicating): Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Vaccines (Non-Live/Inactivated/Non-Replicating). Management: Give non-live/inactivated/non-replicating vaccines at least 2 weeks prior to starting chemotherapy when possible. Patients vaccinated less than 14 days before or during chemotherapy should be revaccinated at least 3 months after therapy is complete. Risk D: Consider therapy modification
Vitamin K Antagonists (eg, warfarin): Mercaptopurine may diminish the anticoagulant effect of Vitamin K Antagonists. Risk C: Monitor therapy
Yellow Fever Vaccine: Immunosuppressants (Cytotoxic Chemotherapy) may enhance the adverse/toxic effect of Yellow Fever Vaccine. Specifically, the risk of vaccine-associated infection may be increased. Immunosuppressants (Cytotoxic Chemotherapy) may diminish the therapeutic effect of Yellow Fever Vaccine. Risk X: Avoid combination
Verify pregnancy status in patients who could become pregnant prior to initiating therapy.
Mercaptopurine is approved for use as part of combination maintenance therapy for acute lymphoblastic leukemia. Product labeling recommends patients who could become pregnant use effective contraception during mercaptopurine treatment and for 6 months after the last mercaptopurine dose. Patients with partners who could become pregnant should be advised to use effective contraception during therapy and for 3 months after the last dose of mercaptopurine.
Mercaptopurine is also used (off label) for the treatment of ulcerative colitis and Crohn disease; monotherapy use for these indications may be continued in patients planning a pregnancy (Bermejo 2018). Mercaptopurine does not decrease fertility in patients with inflammatory bowel disease (AGA [Mahadevan 2019]; Bermejo 2018).
The 6-methylmercaptopurine (6-MMP) and 6-thioguanine (6-TGN) metabolites can be detected in cord blood following maternal use during pregnancy. Infant serum concentrations were undetectable by 6 weeks of age in one study (Flanagan 2021).
Mercaptopurine may be associated with adverse fetal outcomes. An increased risk of miscarriage has been noted with mercaptopurine administration during the first trimester; adverse events, including miscarriage and stillbirth, have also been noted with second and third trimester use. An increased risk of stillbirth, preterm birth, and infants large for gestational age may be observed with maternal use of thiopurines (Meyer 2021).
Intrahepatic cholestasis of pregnancy (ICP) has been associated with thiopurine use. In one study, patients with a metabolite ratio of 6-MMP to 6-TGN >11 (referred to as thiopurine shunting) was associated with the risk of ICP (Prentice 2024). The pharmacokinetic properties of thiopurines may be altered by pregnancy. A decrease in 6-TGN and an increase in 6-MMP was observed in the second trimester (Flanagan 2021). Closely monitor liver transaminases and thiopurine metabolites during pregnancy. Split dosing (taking half the total daily dose every 12 hours) may also prevent shunting (Prentice 2024). Patients with symptoms of ICP and elevated bile acid levels should discontinue treatment. Symptoms improve after the thiopurine is discontinued (FDA 2024).
Mercaptopurine is approved for use as part of combination therapy for acute lymphoblastic leukemia. Data are available following use for leukemia during pregnancy; outcomes may be influenced by concomitant medications (NTP 2013; Ticku 2013).
Mercaptopurine is also used (off label) for the treatment of ulcerative colitis and Crohn disease. The risk of adverse fetal events is decreased with monotherapy. In addition, maternal use to maintain remission may improve pregnancy outcomes. Patients with inflammatory bowel disease who are on maintenance therapy with mercaptopurine monotherapy may continue treatment during pregnancy. Initiating treatment during pregnancy is not recommended. Combination therapy is also not recommended (AGA [Mahadevan 2019]; Puchner 2019; Restellini 2020).
The European Society for Medical Oncology has published guidelines for diagnosis, treatment, and follow-up of cancer during pregnancy; the guidelines recommend referral to a facility with expertise in cancer during pregnancy and encourage a multidisciplinary team (obstetrician, neonatologist, oncology team). In general, if chemotherapy is indicated, it should be avoided in the first trimester and there should be a 3-week time period between the last chemotherapy dose and anticipated delivery, and chemotherapy should not be administered beyond week 33 of gestation (Peccatori 2013).
Mercaptopurine may be present in breast milk.
A case report describes maternal use of mercaptopurine 50 mg daily for the treatment of Crohn disease throughout pregnancy. One month prior to delivery, intracellular concentrations of 6-thioguanine and 6-methylmercaptopurine (6MMP) were detected in maternal blood samples obtained 2 and 4 hours after a maternal dose. A single breast milk sample was obtained 1 day after delivery, 4 hours after the maternal mercaptopurine dose. Mercaptopurine, 6-thioguanine, and 6MMP were undetectable in the breast milk sample (Ter Horst 2019). Mercaptopurine is the active metabolite of azathioprine. Following administration of azathioprine, mercaptopurine can be detected in breast milk (Gardiner 2006).
Due to the potential for serious adverse reactions in the breastfed infant, breastfeeding is not recommended by the manufacturer during therapy and for 1 week after the last mercaptopurine dose. When used as monotherapy for the treatment of inflammatory bowel disease, mercaptopurine is considered to be compatible with breastfeeding (AGA [Mahadevan 2019]; Bermejo 2018). Waiting for 4 hours after the maternal dose to breastfeed may decrease potential exposure to the infant (Puchner 2019; Restellini 2020; ter Horst 2019).
CBC with differential (weekly initially, although clinical status may require increased frequency), bone marrow exam (to evaluate leukemia status and marrow cellularity in patients with prolonged or repeated myelosuppression), liver function tests (transaminases, alkaline phosphatase, and bilirubin; weekly initially, then monthly; monitor more frequently if on concomitant hepatotoxic agents or in patients with preexisting hepatic impairment), renal function, urinalysis. Evaluate pregnancy status prior to use in patients who could become pregnant. Monitor for signs/symptoms of macrophage activating syndrome or photosensitivity reactions. Monitor adherence.
Thiopurine S-methyltransferase (TPMT) genotyping or phenotyping: Consider testing for TPMT deficiency, particularly in patients with abnormally low CBC unresponsive to dose reduction. TPMT genotyping or phenotyping may assist in identifying patients at risk for developing toxicity (Relling 2019).
Nudix hydrolase 15 (NUDT15) genotyping: Consider genotyping for NUDT15 deficiency in patients who experience severe bone marrow toxicities or repeated myelosuppressive episodes. NUDT15 genotyping may assist in identifying patients at risk for developing toxicity (Relling 2019).
Crohn disease or ulcerative colitis (off-label uses): Monitor CBC with differential weekly for 1 month, then biweekly for 1 month, followed by monitoring every 1 to 2 months throughout the course of therapy. LFTs should be assessed every 3 months. Monitor for signs/symptoms of malignancy (eg, splenomegaly, hepatomegaly, abdominal pain, persistent fever, night sweats, weight loss).
Oncology uses: The American Society of Clinical Oncology hepatitis B virus (HBV) screening and management provisional clinical opinion (ASCO [Hwang 2020]) recommends HBV screening with hepatitis B surface antigen, hepatitis B core antibody, total Ig or IgG, and antibody to hepatitis B surface antigen prior to beginning (or at the beginning of) systemic anticancer therapy; do not delay treatment for screening/results. Detection of chronic or past HBV infection requires a risk assessment to determine antiviral prophylaxis requirements, monitoring, and follow-up.
Mercaptopurine is a purine antagonist which inhibits DNA and RNA synthesis; acts as false metabolite and is incorporated into DNA and RNA, eventually inhibiting their synthesis; specific for the S phase of the cell cycle
Absorption: Variable and incomplete (~50% of a dose is absorbed); Cmax of suspension is 34% higher than the tablet.
Distribution: Vd: ~0.9 L/kg; CNS penetration is poor.
Protein binding: ~19%.
Metabolism: Hepatic and in GI mucosa; hepatically via xanthine oxidase and methylation via thiopurine methyltransferase to sulfate conjugates, 6-thiouric acid, and other inactive compounds; first-pass effect.
Half-life elimination: Suspension: Median: 1.3 hours (range: 0.9 to 5.4 hours).
Time to peak, serum: Suspension: Median: Children: 1 to 3 hours, Adults: 0.75 hours (range: 0.33 to 2.5 hours).
Excretion: Urine (46% as mercaptopurine and metabolites).
Altered kidney function: Renal impairment may result in slower elimination of parent drug and metabolites, and a greater cumulative effect.
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