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Side Effects of Mercaptopurine (Purinethol, Purixan)


Side Effects of Mercaptopurine (Purinethol)

Mercaptopurine, known as the brand Purinethol, is a nucleoside metabolic inhibitor used for the maintenance therapy of acute lymphatic (lymphocytic, lymphoblastic) leukemia as part of a combination treatment.

Precautions Before Taking Purinethol

The FDA reports Purinethol is harmful to the liver. Deaths have been attributed to hepatic necrosis (death of liver cells) combined with Purinethol treatment. Hepatic injury can occur with Purinethol dosage, but seems to occur more when recommended dosage is exceeded. There is a risk of infection with live virus vaccines because Purinethol is immunosuppressive. Purinethol may impair the immune response to infectious agents or vaccines.


Purinethol given to a pregnant woman may cause harm to the unborn baby. Women receiving Purinethol have an increased risk of abortion and stillbirth.

Serious Side Effects

Severe side effects of Purinethol are:


  • Myelosuppression (decreased bone marrow activity)
  • Anemia (low number of red blood cells)
  • Neutropenia (low number of white cells)
  • Lymphopenia (low level of lymphocytes)
  • Thrombocytopenia (low blood platelet count)

(Purinethol label reported by the FDA).


The most consistent toxicity of is bone marrow suppression. The risk of this can be increased by thrombocytopenia, anemia, leukopenia, or any combination of these.

Common Side Effects

The most common adverse reactions, according to the FDA, are anorexia, nausea, vomiting, diarrhea, malaise, and rash.


Rare adverse reactions include: oral lesions, hives, elevated transaminases (can lead to severe liver damage), hyperuricemia (high uric acid in the blood), hyperbilirubinemia (abnormal level of bilirubin in the blood), pancreatitis (inflammation of the pancreas), and hyperpigmentation (patches of dark skin).


Other reactions include hepatic fibrosis (excessive number of scarred tissues in the liver), alopecia (sudden hair loss), pulmonary fibrosis (lung tissue becomes scarred), and oligospermia (low sperm count).

About Pharmacogenetic Testing

Individuals who are homozygous for an inherited defect in the TPMT (thiopurine-S-methyltransferase) gene are particularly susceptible to the myelosuppressive effects of Purinethol. They are prone to developing rapid bone marrow suppression once starting Purinethol treatment. Patients with low or intermediate TPMT enzyme activity are more susceptible to hematologic toxicity than patients with normal TPMT activity. Substantial dose reductions are generally required for homozygous-TPMT deficient patients (those with two non-functional alleles) to avoid the development of life threatening bone marrow suppression.

Know Your Risk with the Rxight® Genetic Test

The Rxight® genetic test developed by MD Labs can identify the variations in your genes. Your healthcare provider will be able to understand how your body responds to certain medications and prescribe the right medications decreasing adverse reactions. Rxight® results will give your healthcare provider the ability to make better decisions for your treatment plan.


Call us to learn more about Rxight® at 1-888-888-1932 or email us at support@Rxight.com.


Contributors to this Article:
Michael Sapko, MD, PhD; and Deborah Kallick, PhD, Medicinal Chemistry

Read more about Rxight® Genetic Testing Labs