Common brand names

• Purinethol
• Purixan

How it is administered

Mercaptopurine is taken by mouth, either as a tablet (usually 50 mg) or as an oral suspension (liquid) with a concentration of 20 mg/mL. The oral suspension should be shaken vigorously for at least 30 seconds before use to ensure it is well mixed. It can be taken with or without food, but it is important to be consistent in how you take it each day.

For patients who cannot swallow tablets, the oral suspension is a good alternative. Special care should be taken in measuring the correct dose using the provided oral syringes. The medication should be used within 8 weeks after opening and any remaining suspension should be properly discarded after this period.

How it works

Mercaptopurine is a type of chemotherapy known as a nucleoside metabolic inhibitor. It works by interfering with the growth of cancer cells, specifically by mimicking natural substances (purines) that cells need to make DNA and RNA. When cancer cells take up mercaptopurine, it is converted inside the cell into active metabolites called thioguanine nucleotides (TGNs).

These TGNs are incorporated into the DNA and RNA of the cancer cells, which disrupts their normal function and leads to cell-cycle arrest and cell death. Mercaptopurine also blocks the formation of new purines, further limiting the ability of cancer cells to grow and multiply. This action is especially effective against rapidly dividing cells, such as those found in blood cancers like leukemia.

Who should take it

Mercaptopurine is used as part of a combination chemotherapy maintenance regimen for patients with acute lymphoblastic leukemia (ALL), including children and adults. While it is not specifically approved for Juvenile Myelomonocytic Leukemia (JMML), it may be used in certain blood cancers as determined by your healthcare provider.

The medication is suitable for both pediatric and adult patients, and its safety and effectiveness have been established in children. Your doctor will determine the appropriate dose based on your weight, age, and overall health, as well as how your body responds to the medication.

Who should not take it

There are no absolute contraindications listed for mercaptopurine, but it should be used with caution in certain situations. Patients with a known deficiency in the enzymes TPMT or NUDT15 may be at higher risk for severe side effects and may require significant dose reductions. It should not be used in patients who are pregnant unless absolutely necessary, as it can cause harm to an unborn baby.

People with severe liver or kidney impairment should use the lowest recommended starting dose, and those who are unable to swallow tablets should use the oral suspension. Always inform your doctor of any other medications or health conditions before starting mercaptopurine.

Commonly used with

Mercaptopurine is usually used as part of a combination chemotherapy regimen. It is commonly given with other medications such as methotrexate, vincristine, corticosteroids (like prednisone or dexamethasone), and sometimes with allopurinol (with dose adjustment).

When used with other myelosuppressive or hepatotoxic drugs, close monitoring is required due to increased risk of side effects.

Commonly tested with

Mercaptopurine is often tested in combination with other chemotherapy agents, especially methotrexate, as part of maintenance therapy for leukemia. It may also be studied with drugs that affect its metabolism, such as allopurinol, or with antibiotics like trimethoprim-sulfamethoxazole, which can increase the risk of myelosuppression.

Testing for TPMT and NUDT15 enzyme activity may be recommended before starting therapy to determine the safest dose for each patient.