How it is administered

Mercaptopurine is taken by mouth, either as a tablet (50 mg strength) or as an oral suspension (liquid, 20 mg/mL). The medication should be taken once daily, at the same time each day, either consistently with or without food. The oral suspension should be shaken vigorously for at least 30 seconds before use. It is important to use the provided oral syringe for accurate dosing and to follow all instructions for handling and disposal, as mercaptopurine is a hazardous drug.

How it works

Mercaptopurine is a type of chemotherapy known as a nucleoside metabolic inhibitor. It works by mimicking natural substances (purines) that cells need to make DNA and RNA. Once inside the body, mercaptopurine is converted into active metabolites, including thioguanine nucleotides (TGNs). These metabolites are incorporated into the DNA and RNA of rapidly dividing cells, such as leukemia cells, leading to cell-cycle arrest and cell death. Mercaptopurine also inhibits the formation of new purines, further disrupting the ability of cancer cells to grow and multiply.

Because it targets rapidly dividing cells, mercaptopurine is particularly effective against blood cancers like acute lymphoblastic leukemia (ALL), where abnormal white blood cells multiply uncontrollably. However, it can also affect normal cells that divide quickly, which is why careful monitoring is needed during treatment.

Who Should take it

Mercaptopurine is used as part of a combination chemotherapy maintenance regimen for both adults and children with acute lymphoblastic leukemia (ALL). It is typically given during the maintenance phase of ALL treatment, after initial intensive therapy, to help keep the leukemia in remission and prevent relapse.

Your doctor will determine the exact dose and schedule based on your weight, overall health, and how well your blood counts recover during treatment. Mercaptopurine may also be used in other blood cancers as determined by your healthcare team.

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 known hypersensitivity to mercaptopurine or any of its ingredients should not take it. It is not recommended for use in patients who are pregnant, as it can cause harm to an unborn baby, including miscarriage and birth defects. Women of childbearing age should use effective contraception during treatment and for 6 months after the last dose, and men with female partners should use contraception during treatment and for 3 months after the last dose.

Mercaptopurine should be used cautiously in patients with liver or kidney impairment, and the dose may need to be adjusted. It should not be used in combination with live vaccines due to the risk of infection. Patients with certain genetic enzyme deficiencies (TPMT or NUDT15) may be at higher risk for severe side effects and may require lower doses.

Commonly used with

Mercaptopurine is almost always used as part of a combination chemotherapy regimen for acute lymphoblastic leukemia (ALL). It is commonly given with other medications such as methotrexate, vincristine, corticosteroids (like prednisone or dexamethasone), and sometimes with cytarabine or other agents. The combination is tailored to maximize effectiveness and minimize resistance.

Commonly tested with

Mercaptopurine is frequently studied and used in combination with methotrexate, as this pairing is standard in ALL maintenance therapy. It may also be tested with other chemotherapy agents, immunosuppressants, or targeted therapies in clinical trials for blood cancers. Genetic testing for TPMT and NUDT15 enzyme activity is often performed before or during treatment to guide dosing and reduce the risk of severe side effects.