Mercaptopurine
Pronunciation: (mer-kap-toe-PYOOR-een).
- Generic name
- mercaptopurine
- Brand names
- Purinethol, Purixan, Xaluprine
- Drug class
- Cancer & Oncology
Availability and supply rules vary by country
Trade names by country: United States · Canada
Australia: · Full directory
What mercaptopurine is and how it works
Uses, formulations, monitoring, and supply rules can differ by patient, product, and country. Follow the exact local product information and professional advice.
Mechanism of action: how mercaptopurine works
Mercaptopurine is a purine antagonist that inhibits DNA and RNA synthesis by incorporating false nucleotides into the genetic material of rapidly dividing cells. It is converted intracellularly to thioinosinic acid, which inhibits several enzymes involved in purine metabolism, leading to cytotoxicity in proliferating cells. (1) (2)
What mercaptopurine is used for
Acute Lymphoblastic Leukemia (ALL)
This is the only FDA-approved indication for mercaptopurine: treatment of acute lymphoblastic leukemia as part of a combination chemotherapy maintenance regimen, in adult and pediatric patients. (2)
Crohn's disease and ulcerative colitis (off-label use)
Mercaptopurine is not FDA-approved for Crohn's disease or ulcerative colitis. It is sometimes prescribed off-label for these conditions, a well-established but unapproved use; this is a clinician decision, not a labeled indication. (2)
Before taking mercaptopurine
Do not take / not appropriate for
- Contraindicated in patients with hypersensitivity to mercaptopurine or thioguanine. (Contraindication) (2)
- Avoid use in pregnancy unless benefits outweigh risks. (Contraindication) (2)
Tell your clinician about
(2)How to take mercaptopurine
- General Instructions: Take mercaptopurine exactly as prescribed by your doctor, usually once daily. Take at the same time each day, with or without food, but be consistent in your choice.. Adult Dosing: Typical adult dose for acute lymphoblastic leukemia: 2.5 mg/kg orally once daily. Dosage may be adjusted based on response and tolerance.. Pediatric Dosing: Children are usually dosed at 2.5 mg/kg orally once daily, with adjustments based on clinical response and blood counts.. Administration: Swallow tablets whole with a glass of water. Do not crush or chew. If using the oral suspension, measure the dose carefully with a dosing syringe or spoon.. When To Stop: Do not stop taking mercaptopurine without your doctor's advice. Your doctor will decide when it is safe to stop, based on your condition and response.. Storage: Store at room temperature, away from moisture and heat. Keep out of reach of children.
- This page does not provide a dose calculator. Dosing must follow the prescriber, pharmacist, or product label.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (2)
Missed dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and resume your regular schedule. Do not double up doses.
Overdose
In case of overdose, seek emergency medical attention immediately. Symptoms may include severe nausea, vomiting, diarrhea, mouth sores, unusual bleeding or bruising, and signs of infection. Hospitalization and supportive care may be required. (2)
Side effects
Side effects and their urgency vary; report severe, persistent, or concerning symptoms to a healthcare professional.
Bone marrow suppression
Incidence: Reported in the clinician-authored database; frequency not established
Nausea and vomiting
Incidence: Reported in the clinician-authored database; frequency not established
Diarrhea
Incidence: Reported in the clinician-authored database; frequency not established
Liver toxicity
Incidence: Reported in the clinician-authored database; frequency not established
Mouth sores (stomatitis)
Incidence: Reported in the clinician-authored database; frequency not established
Hair loss
Incidence: Reported in the clinician-authored database; frequency not established
Increased risk of infection
Incidence: Reported in the clinician-authored database; frequency not established
Serious warnings
Mercaptopurine can cause serious bone marrow suppression — serious
Symptoms: Mercaptopurine can cause serious bone marrow suppression. Risk of severe infections due to immunosuppression. May cause liver toxicity; regular liver function tests are required. Increased risk of secondary malignancies with long-term use. Use with caution in patients with TPMT or NUDT15 deficiency.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (2)
Contraindications recorded in the clinician database — serious
Symptoms: Contraindications recorded in the clinician database: Contraindicated in patients with hypersensitivity to mercaptopurine or thioguanine. Use with caution in patients with hepatic or renal impairment, TPMT or NUDT15 deficiency, or a history of myelosuppression. Avoid use in pregnancy unless benefits outweigh risks.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (2)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Recorded interactions | Mercaptopurine may interact with allopurinol (increases toxicity risk), warfarin (reduces anticoagulant effect), and other drugs that affect bone marrow function. Avoid using with other immunosuppressants unless directed by your doctor. Inform your healthcare provider about all medications and supplements you are taking. | (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
Mercaptopurine can cause fetal harm and is generally avoided in pregnancy. Females of reproductive potential are advised to use effective contraception during treatment and for 6 months after the last dose. If you are pregnant, planning to become pregnant, or become pregnant during treatment, seek medical advice promptly. (2)
Breastfeeding
Evidence on breastfeeding during mercaptopurine treatment is mixed: some professional guidelines consider it acceptable in the inflammatory bowel disease setting with infant monitoring, while other sources consider antineoplastic-dose use incompatible with breastfeeding. This is an individualised decision — discuss your specific treatment, dose, and indication with your healthcare provider before breastfeeding. (2)
Children
Approved for pediatric patients with acute lymphoblastic leukemia as part of combination chemotherapy. Weight-based dosing is generally 1.5 to 2.5 mg/kg/day given once daily, with a maximum daily dose of 150 mg and maximum single dose of 2.5 mg/kg, adjusted by the treating oncologist based on clinical response and blood counts. (2)
Renal_impairment
The FDA label directs prescribers to give specific dose modifications for organ impairment; this is not a self-adjustment — your treating clinician selects and reviews your dose. Renal impairment: the label states prescribers should use the lowest recommended starting dose of mercaptopurine, or increase the dosing interval to every 36-48 hours, in patients with renal impairment (creatinine clearance below 50 mL/min), then adjust further to maintain a desirable absolute neutrophil count (ANC) and for adverse reactions. Hepatic impairment: the label states prescribers should use the lowest recommended starting dose in patients with hepatic impairment, adjusting further to maintain ANC and for adverse reactions. In overdose, dialysis is not expected to meaningfully clear mercaptopurine because it is rapidly taken up into cells; seek emergency medical attention rather than attempting to manage an overdose at home. (2)
Hepatic_impairment
The FDA label directs prescribers to give specific dose modifications for organ impairment; this is not a self-adjustment — your treating clinician selects and reviews your dose. Renal impairment: the label states prescribers should use the lowest recommended starting dose of mercaptopurine, or increase the dosing interval to every 36-48 hours, in patients with renal impairment (creatinine clearance below 50 mL/min), then adjust further to maintain a desirable absolute neutrophil count (ANC) and for adverse reactions. Hepatic impairment: the label states prescribers should use the lowest recommended starting dose in patients with hepatic impairment, adjusting further to maintain ANC and for adverse reactions. In overdose, dialysis is not expected to meaningfully clear mercaptopurine because it is rapidly taken up into cells; seek emergency medical attention rather than attempting to manage an overdose at home. (2)
Monitoring
(2)Storage
Store at room temperature, away from moisture and heat. Keep out of reach of children.
Professional information
Clinician-facing context only. This section does not replace current product labeling.
General
Indication: Acute Lymphocytic Leukemia (ALL)
Dose summary: Initial dose is typically 1.5 to 2.5 mg/kg/day, adjusted based on clinical response and tolerance.
Renal context: The FDA label directs prescribers to use the lowest recommended starting dose of mercaptopurine, or to increase the dosing interval to every 36-48 hours, in patients with renal impairment (creatinine clearance below 50 mL/min), then adjust further to maintain a desirable absolute neutrophil count (ANC) and for adverse reactions. (1) (2)
Hepatic guidance
The FDA label directs prescribers to use the lowest recommended starting dose of mercaptopurine in patients with hepatic impairment, then adjust further to maintain a desirable absolute neutrophil count (ANC) and for adverse reactions.
Frequently asked questions
What is mercaptopurine (6-MP) used for?
Mercaptopurine's only FDA-approved use is treatment of acute lymphoblastic leukemia (ALL) as part of combination chemotherapy. It is sometimes prescribed off-label by specialists for inflammatory bowel conditions such as Crohn's disease or ulcerative colitis.
How does mercaptopurine work?
Mercaptopurine works by interfering with the DNA and RNA synthesis of rapidly dividing cells, such as cancer cells, slowing or stopping their growth.
What should I do if I miss a dose?
Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose. Do not take two doses at once.
Can I take mercaptopurine during pregnancy?
Mercaptopurine may harm an unborn baby. Inform your doctor if you are pregnant or planning to become pregnant. Effective contraception is recommended during treatment.
What are the most serious side effects?
Serious side effects include bone marrow suppression (low blood counts), severe infections, liver toxicity, and allergic reactions. Contact your doctor immediately if you notice unusual bruising, bleeding, persistent fever, or yellowing of the skin or eyes.
Are there any foods or medicines I should avoid?
Avoid live vaccines, alcohol, and medications that may interact with mercaptopurine, such as allopurinol. Always consult your doctor before starting new medications.
How often will I need blood tests while taking mercaptopurine?
Frequent blood tests are required, especially at the start of treatment, to monitor your blood cell counts and liver function.
What happens if I take too much Mercaptopurine (6-MP)?
Taking too much Mercaptopurine (6-MP) can lead to severe side effects such as bone marrow suppression, liver damage, and gastrointestinal toxicity. Symptoms may include unusual bleeding or bruising, severe fatigue, or jaundice. If you suspect an overdose, seek immediate emergency medical attention or contact your local poison control center.
Can I drink alcohol while taking Mercaptopurine (6-MP)?
It is generally advised to avoid or significantly limit alcohol consumption while taking Mercaptopurine (6-MP). Both alcohol and Mercaptopurine can be metabolized by the liver, and their combined use may increase the risk of liver damage or exacerbate existing liver issues. Always consult your healthcare provider for personalized advice regarding alcohol intake.
Is Mercaptopurine (6-MP) safe during pregnancy?
Mercaptopurine (6-MP) is generally not recommended during pregnancy due to potential risks to the developing fetus. It falls under a pregnancy category that indicates potential harm. If you are pregnant, planning to become pregnant, or breastfeeding, it is crucial to discuss the risks and benefits with your healthcare provider to determine the safest course of action.
What is the mechanism of action of mercaptopurine?
Mercaptopurine is a purine antagonist that inhibits DNA and RNA synthesis by incorporating false nucleotides into the genetic material of rapidly dividing cells. It is converted intracellularly to thioinosinic acid, which inhibits several enzymes involved in purine metabolism, leading to cytotoxicity in proliferating cells. (1) (2)
What is the generic name of Mercaptopurine?
The generic name is mercaptopurine. It is sold under brand names including Purinethol, Purixan, Xaluprine.
What class of drug is mercaptopurine?
Mercaptopurine is classed as: Cancer & Oncology.
References
- Mercaptopurine (6-MP) – MedGuideGlobal Medicine RecordMedGuideGlobal clinician-authored medicine record (internal database) · Worldwide (internal reference) · accessed 2026-08-06 · source 1
- Mercaptopurine – FDA prescribing information (DailyMed)U.S. Food and Drug Administration / DailyMed · United States · dated Not specified (retrieved 2026-08-06) · accessed 2026-08-06 · source 2
- MERCAPTOPURINE SUSPENSION [HIKMA PHARMACEUTICALS USA INC.] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 3
- Mercaptopurine — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 4
- MERCAPTOPURINE — FDA approval record (Drugs@FDA ANDA216418)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 5
- mercaptopurine — RxNorm normalized drug concept (RXCUI 103)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 6
Brand names by country
Single-ingredient mercaptopurine names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- PURIXAN20 mg/mL · nova laboratories, ltd
Canada
- PURINETHOL