TM Owner Stason Pharmaceuticals, Inc. (US); Aspen Bad Oldesloe GmbH (EU, as Puri-Nethol)
Purinethol 50mg Tablet
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Indications & Clinical Uses
- Purinethol 50 mg (mercaptopurine) is a thiopurine antimetabolite chemotherapy tablet, an analogue of the purine base hypoxanthine that interferes with DNA and RNA synthesis in dividing cells.
- In the United States it is approved for adults and children with acute lymphoblastic leukaemia (ALL), used as part of a combination chemotherapy maintenance regimen once remission has been achieved with other drugs; it is not a stand-alone induction treatment.
- In the European Union and UK the same molecule is sold as Puri-Nethol, with the same ALL maintenance use, and mercaptopurine is also used off-label for inflammatory bowel disease in some countries.
- It should not be confused with Purixan, the same active substance as an oral liquid suspension rather than a tablet - the two are not automatically interchangeable dose-for-dose without checking strength.
- Treatment is prescribed and monitored only by a specialist in cancer or blood disorders.
Side Effects
- Myelosuppression - low white blood cells, low platelets, and anaemia - affects more than 1 in 10 people taking Purinethol and is the most common reaction; regular blood counts are needed to catch it early.
- Common reactions also include loss of appetite, nausea, vomiting, diarrhoea, general malaise, and skin rash.
- Seek urgent medical attention for signs of infection (fever, sore throat, chills), unusual bruising or bleeding, or yellowing of the skin or eyes (jaundice), which can signal potentially fatal liver damage (hepatotoxicity) - liver tests are checked regularly during treatment.
- Rarely, mercaptopurine has been linked to secondary cancers, including hepatosplenic T-cell lymphoma (mainly reported with related thiopurines in combination therapy), and to macrophage activation syndrome, a serious overactive immune reaction.
- Purinethol does not carry a current FDA boxed warning, but these serious risks still require close specialist monitoring throughout treatment.
Precautions & Warnings
- Before starting Purinethol, TPMT and NUDT15 genetic testing is recommended, as patients with reduced enzyme activity are at much higher risk of severe myelosuppression and usually need a lower starting dose; testing should also follow any unexpectedly severe drop in blood counts.
- Full blood counts and liver function tests are monitored regularly throughout treatment, and doses are adjusted or paused for significant myelosuppression or liver toxicity.
- Purinethol can cause fetal harm: women should use effective contraception during treatment and for some time afterwards, and should discuss pregnancy plans with their specialist before starting or stopping treatment; the effect on breastfed infants is not established, so breastfeeding is generally avoided.
- Vaccination with live vaccines should be discussed with the treating specialist, since mercaptopurine suppresses the immune response.
- There are no specific driving restrictions, but report severe fatigue or illness before driving.
Avoid Interactions
- Allopurinol and other xanthine oxidase inhibitors block the breakdown of mercaptopurine and can cause severe, potentially fatal toxicity; if allopurinol must be co-prescribed, the Purinethol dose is reduced to about one-quarter to one-third of the usual amount under close monitoring.
- Warfarin and other coumarin anticoagulants may have reduced effect when combined with mercaptopurine, so anticoagulation should be checked more closely.
- Other drugs that suppress bone marrow, including aminosalicylates such as sulfasalazine, mesalazine and olsalazine, can add to the myelosuppressive effect of Purinethol and increase the risk of low blood counts.
- Combining Purinethol with other immunosuppressive medicines increases the risk of infection.
- Tell your healthcare provider about every medicine, herbal remedy and supplement you take, including over-the-counter products, before starting or while taking Purinethol, and mention any planned vaccinations.
References
Frequently Asked Questions
Purinethol (mercaptopurine) is a chemotherapy tablet used to keep acute lymphoblastic leukaemia (ALL) in remission, as part of a combination maintenance regimen in adults and children. It is given after remission is first achieved with other treatment, not as the initial therapy.
Purinethol is taken as a tablet by mouth, usually once daily, with your dose based on your body weight and blood counts. Your specialist may adjust the dose over time, especially if you take allopurinol or have reduced TPMT or NUDT15 enzyme activity.
Low blood counts (affecting more than 1 in 10 people), loss of appetite, nausea, vomiting, and diarrhoea are common with Purinethol. Get urgent help for fever or signs of infection, unusual bruising or bleeding, or yellowing skin or eyes, which can mean serious liver damage.
Avoid allopurinol unless your specialist reduces your Purinethol dose, since it raises mercaptopurine levels and toxicity risk. Tell your care team about all other medicines, especially warfarin and aminosalicylates like mesalazine, and discuss any vaccinations, since Purinethol weakens your immune response.
Yes. TPMT and NUDT15 enzyme testing is recommended before starting Purinethol, since low activity raises the risk of severe, even life-threatening, bone marrow suppression. Your specialist will use the result to guide your starting dose and how closely your blood counts are monitored.
No. Purinethol can cause fetal harm, so women need effective contraception during treatment and should discuss pregnancy plans with their specialist beforehand. Breastfeeding is generally avoided during treatment, as it is not known if mercaptopurine passes into breast milk.

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