Mercaptopurine

Introduction

Written by Ashley Wong, PharmD
Medically reviewed by Dena Westphalen, PharmD
Updated on September 7, 2023

Mercaptopurine (mer kap toe PURE een) is a generic medication prescribed for acute lymphoblastic leukemia (ALL). Mercaptopurine belongs to a group of chemotherapy drugs called antimetabolites.

Side effects of mercaptopurine

Mercaptopurine may cause mild or serious side effects. More common mild side effects of mercaptopurine and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about mercaptopurine’s side effects, ask your doctor or pharmacist. You can also refer to the prescribing information for mercaptopurine listed in the “Resources” section.

Mild side effects

More common mild side effects reported with mercaptopurine are listed below.

This article doesn’t include all possible mild side effects of the drug. To learn more about mercaptopurine’s side effects, refer to the prescribing information for mercaptopurine listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Mercaptopurine oral tablet’s mild side effects include:

• loss of appetite
• nausea
• vomiting
• diarrhea
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for mercaptopurine” section.

Serious side effects

Serious side effects of mercaptopurine are listed below.

This article doesn’t include all possible serious side effects of the drug. To learn more about mercaptopurine’s side effects, refer to the prescribing information for mercaptopurine listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, mercaptopurine’s serious side effects include:

• myelosuppression (low blood cell counts)
• hyperuricemia (high uric acid levels)
• hyperbilirubinemia (high bilirubin levels)
• pancreatitis (inflammation of the pancreas)
• liver damage
• infections
• hair loss
• lung problems
• low sperm count
• cancer other than the cancer mercaptopurine is prescribed to treat
• sensitivity to sunlight
• low blood sugar
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for mercaptopurine” section.

Common questions about mercaptopurine

Below, you’ll find answers to a few commonly asked questions about mercaptopurine.

Can mercaptopurine be used for ulcerative colitis?

Maybe, but mercaptopurine is only approved to treat a type of cancer called acute lymphoblastic leukemia (ALL). It’s not approved to treat ulcerative colitis.

In some cases, doctors may prescribe mercaptopurine “off-label” for ulcerative colitis or other conditions. With off-label use, doctors prescribe a drug for a purpose other than what it’s approved for.

If you have questions about treatment options for ulcerative colitis, talk with your doctor.

What brand names are available for mercaptopurine?

At this time, mercaptopurine oral tablet is only available as a generic medication. There are no brand-name versions available.

Mercaptopurine liquid suspension (a type of liquid mixture) is available as a brand-name medication called Purixan. But this form isn’t available as a generic medication.

A generic medication is an identical copy of the active drug in a brand-name medication. (An active drug is the ingredient that makes a medication work.) Generic drugs are believed to be as effective and safe as brand-name drugs. And generic drugs typically cost less than brand-name drugs.

If you have more questions about this, talk with your doctor or pharmacist.

How does mercaptopurine work? And how long does it take to start working?

Mercaptopurine works to treat acute lymphoblastic leukemia (ALL) by interfering with the way cancer cells grow. Its mechanism of action causes the cancer cells to die and stops their growth.

Mercaptopurine will start working as soon as you start taking it, but it generally takes 3 months or longer to notice this on lab tests. After about 3 months, your doctor may start to see improvements on lab tests used to monitor your condition.

If you’d like to know more about this, talk with your doctor or pharmacist.

Uses of mercaptopurine

The Food and Drug Administration (FDA) approves prescription drugs such as mercaptopurine for certain conditions. An approved use for mercaptopurine is described below.

Use for leukemia

Doctors may prescribe mercaptopurine oral tablet for treating acute lymphoblastic leukemia (ALL). It’s used for this purpose in adults and children. It’s usually prescribed as a long-term treatment.

With ALL, cells in your bone marrow grow out of control. Bone marrow is the spongy part of your bone where new blood cells are made. ALL is an aggressive form of cancer, which means it can progress quickly. It raises your risk of bleeding and developing infections. You may have symptoms such as bleeding from the gums, bruises, and bone pain.

Mercaptopurine is prescribed together with other chemotherapy medications as maintenance treatment for ALL. (Maintenance treatment is given after initial treatment. It helps keep ALL from coming back.)

Interactions and warnings for mercaptopurine

Below, you’ll find information about mercaptopurine’s possible interactions and warnings.

Interactions of mercaptopurine

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take mercaptopurine, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for mercaptopurine” section below.

Warnings for mercaptopurine

Some people should not take mercaptopurine, and others should take it cautiously.

Mercaptopurine could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether mercaptopurine is a safe option for you.

Ask your doctor about specific warnings for mercaptopurine, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Mercaptopurine can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to mercaptopurine or any of its ingredients, your doctor will likely not prescribe mercaptopurine. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to mercaptopurine, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of mercaptopurine

You should not take more mercaptopurine than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much mercaptopurine, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and mercaptopurine

Information about mercaptopurine and pregnancy and breastfeeding is described below.

Mercaptopurine and pregnancy

Mercaptopurine should not be taken during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before taking this medication. Your doctor may suggest birth control options to use during treatment with mercaptopurine.

Mercaptopurine and breastfeeding

Mercaptopurine should not be taken while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before taking this medication. Your doctor may recommend other ways to feed your child during treatment with mercaptopurine.

What to ask your doctor

Let your doctor know if you have questions about mercaptopurine or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• Will mercaptopurine affect my fertility (ability to conceive a child)?
• How will I know if mercaptopurine is working?
• How long can I take mercaptopurine?
• Am I at higher risk of side effects from mercaptopurine than other people?
• Are there any drug interactions I should try to avoid when taking mercaptopurine?

Resources

• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Mercaptopurine tablets, for oral use. (2022). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/15904472-4c32-4224-95d3-eb131a7ff9c8/spl-doc
• Sharma H, et al. (2023). Mercaptopurine. https://www.ncbi.nlm.nih.gov/books/NBK557620/

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.