What is Mercaptopurine: Uses, Dosage, Side Effects and More

Mercaptopurine is a medication that helps control certain types of cancer and autoimmune conditions by slowing down the growth of abnormal cells. This prescription medicine belongs to a group called antimetabolites, which work by interfering with how cells make DNA and RNA. Your doctor might prescribe this medication as part of your treatment plan for leukemia or inflammatory bowel disease.

What is Mercaptopurine?

Mercaptopurine is an oral chemotherapy medication that comes in tablet form. It's designed to target rapidly dividing cells, which includes both cancer cells and some healthy cells in your body. The medication works by mimicking a natural substance your cells need to grow and divide.

This medicine has been used safely for decades to treat various conditions. While it's considered a chemotherapy drug, the doses used are often much lower than what you might imagine from traditional cancer treatments. Your doctor will carefully monitor your response and adjust the dosage as needed.

What is Mercaptopurine Used For?

Mercaptopurine treats acute lymphoblastic leukemia (ALL), a type of blood cancer that affects white blood cells. It's also prescribed for inflammatory bowel diseases like Crohn's disease and ulcerative colitis when other treatments haven't worked well enough.

For leukemia patients, this medication is typically part of a longer treatment plan that includes other medicines. The goal is to help your body eliminate cancer cells and prevent them from coming back. In inflammatory bowel disease, mercaptopurine helps calm down your immune system's overactive response that causes inflammation in your digestive tract.

Sometimes doctors prescribe mercaptopurine for other autoimmune conditions when standard treatments aren't providing enough relief. Your healthcare provider will explain exactly why this medication is right for your specific situation.

How Does Mercaptopurine Work?

Mercaptopurine works by getting incorporated into your cells' DNA and RNA building process. When abnormal cells try to grow and divide, the medication interferes with their ability to copy their genetic material correctly. This causes these problematic cells to die off naturally.

The medication is considered moderately strong, but it's generally well-tolerated when used at appropriate doses. Your body processes mercaptopurine through your liver, where it gets converted into active forms that do the actual work. This process takes time, which is why you might not notice immediate effects.

Because mercaptopurine affects cell division, it can impact both abnormal cells and some healthy cells that naturally divide quickly. This includes cells in your bone marrow, digestive tract, and immune system. Your doctor will monitor these areas closely during treatment.

How Should I Take Mercaptopurine?

Take mercaptopurine exactly as your doctor prescribes, typically once daily on an empty stomach. The best time is usually one hour before eating or two hours after a meal, as food can interfere with how well your body absorbs the medication.

Swallow the tablets whole with a full glass of water. Don't crush, chew, or break them, as this can affect how the medication works. If you have trouble swallowing tablets, talk to your pharmacist about options that might help.

Try to take your medication at the same time each day to maintain steady levels in your bloodstream. Many people find it helpful to set a daily reminder on their phone. If you're taking other medications, check with your doctor about the best timing to avoid interactions.

Avoid drinking alcohol while taking mercaptopurine, as it can increase the risk of liver problems. Also, stay away from grapefruit and grapefruit juice, which can interfere with how your body processes the medication.

How Long Should I Take Mercaptopurine For?

The duration of mercaptopurine treatment varies significantly depending on your condition and how well you respond to the medication. For leukemia, treatment often continues for two to three years as part of a maintenance phase after initial intensive therapy.

If you're taking mercaptopurine for inflammatory bowel disease, you might need it for several months to years. Some people require long-term treatment to keep their condition under control. Your doctor will regularly evaluate whether the medication is still necessary and beneficial for you.

Never stop taking mercaptopurine suddenly without talking to your doctor first. Stopping abruptly could cause your condition to flare up or worsen. If you need to discontinue the medication, your doctor will create a plan to do so safely.

What Are the Side Effects of Mercaptopurine?

Like all medications, mercaptopurine can cause side effects, though not everyone experiences them. Most side effects are manageable and tend to improve as your body adjusts to the medication.

Here are the more common side effects you might experience:

• Nausea and loss of appetite
• Fatigue and weakness
• Increased risk of infections due to lowered white blood cell counts
• Easy bruising or bleeding from low platelet counts
• Mouth sores or ulcers
• Diarrhea or stomach discomfort
• Hair thinning (usually mild)

These common effects often become less bothersome as your treatment continues. Your healthcare team can suggest ways to manage them effectively.

More serious side effects can occur, though they're less common. These require immediate medical attention and include:

• Signs of liver problems like yellowing of skin or eyes, dark urine, or persistent nausea
• Severe infections with fever, chills, or persistent cough
• Unusual bleeding or bruising that doesn't stop
• Severe stomach pain or persistent vomiting
• Allergic reactions with rash, difficulty breathing, or swelling

Your doctor will monitor you closely with regular blood tests to catch any problems early. Don't hesitate to contact your healthcare team if you notice any concerning symptoms.

Some rare but serious side effects include severe bone marrow suppression, liver toxicity, and increased risk of certain cancers with long-term use. Your doctor weighs these risks against the benefits of treatment for your specific condition.

Who Should Not Take Mercaptopurine?

Mercaptopurine isn't suitable for everyone, and your doctor will carefully review your medical history before prescribing it. People with certain genetic variations that affect how they process the medication may need different doses or alternative treatments.

You should not take mercaptopurine if you're allergic to it or similar medications. Tell your doctor about any previous allergic reactions to chemotherapy drugs or other medications. Pregnancy is another important consideration, as mercaptopurine can harm a developing baby.

Certain medical conditions require extra caution or may prevent you from taking mercaptopurine safely:

• Severe liver disease or active hepatitis
• Existing bone marrow disorders
• Active infections that aren't under control
• Kidney disease requiring dose adjustments
• Previous severe reactions to similar medications

If you're planning to become pregnant or are breastfeeding, discuss this with your doctor. Both men and women should use effective birth control during treatment and for some time afterward.

Your doctor will also consider any other medications you're taking, as some drugs can interact with mercaptopurine. This includes certain antibiotics, blood thinners, and other immune-suppressing medications.

Mercaptopurine Brand Names

Mercaptopurine is available under several brand names, with Purinethol being the most commonly recognized. You might also see it referred to as 6-mercaptopurine or 6-MP in medical literature and discussions with your healthcare team.

Generic versions of mercaptopurine are widely available and work just as effectively as brand-name versions. Your pharmacy may substitute the generic form unless your doctor specifically requests the brand name. Both forms contain the same active ingredient and meet the same safety and effectiveness standards.

Mercaptopurine Alternatives

Several alternative medications might be considered if mercaptopurine isn't suitable for you or doesn't work well enough. The choice depends on your specific condition, medical history, and how you've responded to previous treatments.

For inflammatory bowel disease, alternatives include azathioprine (which is closely related to mercaptopurine), methotrexate, or newer biologic medications like infliximab or adalimumab. Each has its own benefits and side effect profile that your doctor will discuss with you.

In cancer treatment, alternatives might include other chemotherapy drugs, targeted therapies, or immunotherapy options. Your oncologist will consider factors like your specific type of cancer, stage of disease, and overall health when recommending alternatives.

The decision to switch medications should always be made in consultation with your healthcare team. They can help you weigh the pros and cons of different options based on your individual situation.

Is Mercaptopurine Better Than Azathioprine?

Mercaptopurine and azathioprine are closely related medications that work in similar ways, but they're not exactly the same. Azathioprine is actually converted to mercaptopurine in your body, so mercaptopurine is the active form that does the actual work.

Neither medication is definitively "better" than the other - the choice depends on your individual circumstances. Some people tolerate one better than the other, while some doctors prefer one based on their experience or specific aspects of your condition.

Azathioprine is often tried first for inflammatory bowel disease because it's been studied extensively for this use. However, mercaptopurine might be preferred if you have certain genetic variations that affect how you process azathioprine. Your doctor can order genetic testing to help guide this decision.

Both medications require similar monitoring and have comparable side effect profiles. The decision between them often comes down to your doctor's preference, your response to treatment, and any specific factors in your medical history.