Mercaptopurine

 

What Is Mercaptopurine?

Mercaptopurine (also called 6-MP) is a prescription medicine that belongs to a drug class called antimetabolites. More specifically, it is a purine analog. It is also considered an immunosuppressant because it lowers the activity of certain immune cells.

Approved Uses

In the United States, mercaptopurine is FDA-approved as part of a combination maintenance treatment plan for acute lymphoblastic leukemia (ALL). ALL is a cancer of the blood and bone marrow.

Other Prescribed Uses

Specialists sometimes prescribe mercaptopurine for conditions that are not listed on the FDA label, such as inflammatory bowel disease (Crohn’s disease and ulcerative colitis). These decisions are made by a specialist who weighs the benefits and risks for each person. This guide does not recommend use for any condition that is not FDA-approved.

Available Formulations and Strengths

• Oral tablets: Mercaptopurine 50mg (scored tablets)
• Oral suspension (liquid): 20 mg per mL (2,000 mg per 100 mL), available under a brand name

Availability of specific products can vary. Your pharmacist can confirm which form you have.

What Is the Recommended Dosage of Mercaptopurine?

There is no single dose that fits everyone. Your specialist decides the dose based on several factors:

• The condition being treated
• Age
• Body weight or body surface area, which is often used for children
• Kidney and liver function
• Blood test results, especially white blood cell counts
• Genetic test results for enzymes called TPMT and NUDT15, which affect how the body processes the drug
• Other medicines being taken at the same time

Available Dosage Forms

Mercaptopurine comes as a tablet and as an oral liquid. The liquid form may be helpful for children or for people who cannot swallow tablets. The two forms are not always measured the same way, so do not switch between them without instructions.

Follow Your Specialist’s Instructions

Doses are often adjusted over time based on lab results. Take mercaptopurine exactly as prescribed. Do not change the dose, split tablets in ways you were not told to, or stop the medicine on your own. Use an oral syringe or measuring device supplied by the pharmacy for the liquid form, not a kitchen spoon.

How Mercaptopurine Works

Cells need building blocks to make new DNA. Mercaptopurine looks similar to one of these natural building blocks (a purine). After the body converts it into active forms, it interferes with the making of DNA and RNA in rapidly dividing cells.

• In leukemia, this helps slow or stop the growth of abnormal blood cells. It is used as part of a larger treatment plan and is not meant to work alone.
• In immune-related conditions, it lowers the activity of certain immune cells that can drive inflammation.

Mercaptopurine is used to control or manage a condition. Whether it leads to remission or long-term control depends on the condition, the full treatment plan, and the individual. It can take weeks to months to see the full effect in some conditions.

Is a Prescription Required to Buy Mercaptopurine Online?

Yes. Mercaptopurine is a prescription-only medicine. It should only be started and monitored by a licensed medical specialist. Depending on the reason for treatment, this may be:

• A pediatric or adult oncologist or hematologist (for leukemia)
• A gastroenterologist (for inflammatory bowel disease)
• Another specialist who is experienced with immunosuppressive medicines

Buying Medicine Safely

• Use only licensed pharmacies that require a valid prescription.
• Be cautious of websites that offer mercaptopurine without a prescription. Products from these sources may be counterfeit, expired, contaminated, or the wrong strength.
• Do not use veterinary products or products from unverified sellers.
• If you are unsure whether a pharmacy is legitimate, check with your local pharmacist or your country’s pharmacy regulator.

Side Effects of Mercaptopurine

Not everyone has side effects, and many people have only mild ones. Your care team will monitor you with regular blood tests.

Common Side Effects

• Nausea or upset stomach
• Vomiting
• Loss of appetite
• Diarrhea
• Mouth sores
• Skin rash
• Tiredness or weakness
• Hair thinning

Serious Side Effects

These are less common but can be serious:

• Low blood cell counts (bone marrow suppression): This can cause infections, easy bruising or bleeding, and severe tiredness or paleness.
• Liver problems: Signs include yellowing of the skin or eyes, dark urine, pain in the upper right abdomen, or swelling of the belly.
• Pancreatitis (inflammation of the pancreas): Signs include severe stomach or back pain, often with nausea and vomiting.
• Serious infections, because the immune system may be weaker
• Increased sensitivity to sunlight and a higher risk of some skin cancers over time
• Increased risk of certain cancers, including lymphoma, with long-term use of immune-suppressing medicines
• Allergic reactions: Signs include swelling of the face, lips, or throat, trouble breathing, or a severe rash.

When to Get Medical Help Right Away

Contact your specialist or seek emergency care if you have:

• Fever, chills, or signs of infection (a fever is always treated as urgent for people on this medicine)
• Unusual bleeding or bruising
• Yellow skin or eyes, or dark urine
• Severe stomach or back pain
• Swelling of the face, lips, or throat, or trouble breathing
• A severe skin reaction or blistering

Drug Interactions

Mercaptopurine can interact with other medicines. Some interactions require a dose change or extra monitoring.

Major Interaction Categories

• Gout medicines: Allopurinol and febuxostat can raise mercaptopurine levels in the body and may increase the risk of serious side effects. Dose changes are often needed.
• Blood thinners: Warfarin’s effect may change, so blood clotting tests may need closer monitoring.
• Other medicines that lower blood counts: Examples include some chemotherapy drugs, trimethoprim-sulfamethoxazole (an antibiotic), and certain antiviral medicines.
• Aminosalicylates: Medicines such as mesalamine, sulfasalazine, and olsalazine may affect how the body processes mercaptopurine.
• Other immune-suppressing medicines: Combining these may raise the risk of infection or other side effects.
• Live vaccines: These are generally avoided during treatment because the immune system may be weakened. Ask your specialist before any vaccination.

Over-the-Counter Medicines

Ask a pharmacist or specialist before using OTC products, including pain relievers, cold and flu products, and antacids.

Supplements and Herbal Products

Vitamins, supplements, and herbal products may also interact with mercaptopurine or affect the liver. Do not start them without checking first.

Share a Full Medication List

Give your licensed medical specialist a complete list of everything you take, including prescription medicines, OTC medicines, supplements, and herbal products. Update the list whenever anything changes.

Safety & Important Considerations

Liver and Kidney Precautions

Mercaptopurine can affect the liver, and the kidneys help clear the medicine from the body. People with liver or kidney disease may need lower doses or closer monitoring.

Genetic Testing

Some people have lower activity of the enzymes TPMT or NUDT15. They can be more likely to have severe drops in blood counts and may need a much lower dose. Testing for these enzymes may be recommended before or during treatment.

Pregnancy and Breastfeeding

• Mercaptopurine can harm an unborn baby. Talk with your specialist about effective birth control before starting treatment, for both women and men who may father a child.
• Tell your specialist right away if you are pregnant, planning pregnancy, or become pregnant.
• Breastfeeding while taking mercaptopurine is generally not advised. Discuss options with your specialist.

Children and Older Adults

• Children: Dosing is often based on body size and is carefully monitored. The liquid form may be used for young children.
• Older adults: They may be more sensitive to side effects and more likely to have reduced kidney or liver function, so closer monitoring may be needed.

Monitoring

Expect regular blood tests, such as complete blood counts and liver function tests. Your specialist may also check kidney function. Do not skip these appointments.

Other Important Safety Points

• Protect your skin: Use sunscreen, wear protective clothing, and limit sun exposure. Have regular skin checks as advised.
• Prevent infection: Wash hands often and avoid close contact with people who are sick.
• Safe handling: Mercaptopurine is a hazardous drug. Caregivers should wash their hands after handling it and avoid touching broken tablets or spilled liquid with bare hands. Pregnant caregivers should ask a pharmacist about safe handling. Follow the pharmacy’s instructions for wiping up spills and disposing of waste.
• Take it consistently: Take it the same way each day, either always with food or always without food, as directed by your specialist.
• FDA information: Mercaptopurine labeling includes warnings about bone marrow suppression, liver injury, immunosuppression, and harm to a developing baby. Read the Medication Guide that comes with your prescription.

Who This Medication Is For

Mercaptopurine is prescribed for people who need treatment for a condition that a specialist has decided it can help manage.

• FDA-approved indication: Acute lymphoblastic leukemia, as part of a combination maintenance regimen. It is used in both children and adults.
• Other uses: Some specialists prescribe it for certain immune-related or inflammatory conditions based on their clinical judgment.

Whether it is right for a particular person depends on their diagnosis, other health conditions, lab results, and other treatments.

Who Should Not Take Mercaptopurine

Mercaptopurine may not be safe for everyone. Tell your specialist before starting if any of the following apply.

• Allergy: You have had a serious allergic reaction to mercaptopurine or any ingredient in the product.
• Pregnancy: You are pregnant or planning to become pregnant, unless your specialist has decided the benefits outweigh the risks.
• Very low TPMT or NUDT15 activity: You may need a substantially lower dose or a different treatment.
• Existing liver disease, kidney disease, or low blood counts: Extra caution and closer monitoring are needed.
• Active serious infection: Treatment may need to be delayed or adjusted.
• Recent or planned live vaccines: Discuss timing with your specialist.

What to Do If You Miss a Dose

• If you remember soon after the missed time, take the dose as directed by your specialist.
• If it is almost time for your next dose, skip the missed dose and go back to your regular schedule.
• Never take a double dose to make up for a missed one.
• If you are unsure what to do, or you miss more than one dose, contact your licensed medical specialist or pharmacist for guidance.
• Keep a simple dose log or use reminders to help stay on schedule.

Related medications to Mercaptopurine

The right alternative depends on the condition being treated. Examples of medicines that may be used in similar situations include:

• For leukemia treatment plans: Other antimetabolite medicines, such as methotrexate or thioguanine, may be part of combination regimens.
• For inflammatory bowel disease: Other immune-modulating medicines, such as azathioprine (a related medicine) or methotrexate, and various biologic therapies may be considered.

These options differ in how they work, their side effects, and their monitoring needs. Do not switch or stop treatment on your own. Any change should be made only after talking with your licensed medical specialist.

Storage Instructions

• Temperature: Store tablets and liquid at room temperature, generally between 68°F and 77°F (20°C to 25°C), unless the label says otherwise.
• Moisture and light: Keep tablets in the original tightly closed container, away from moisture (avoid bathrooms) and direct light.
• Liquid form: Follow the label for shaking the bottle before use, and for how long the bottle may be used after opening. Do not use it past the date given.
• Child safety: Keep all medicines locked or out of reach and sight of children and pets. Use child-resistant caps.
• Disposal: Do not flush or throw away unused medicine in household trash unless instructed. Ask your pharmacist about take-back programs or safe disposal for hazardous drugs.

Disclaimer:

This page is for educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Patients must consult a licensed medical specialist, such as an oncologist, hematologist, or gastroenterologist, depending on the condition being treated, before starting, changing, or stopping treatment. Treatment decisions must be based on a full clinical evaluation by a qualified specialist. If you think you are having a medical emergency, call your local emergency number right away.