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Side Effects of
Purine Antagonists


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Description: Purine antagonists are in a category of medications called “antimetabolites.” They are primarly indicated for the treatment of cancer. Also called “purine receptor agonists,” purine antagonists are pharmacological agents that block the action of chemicals called purines, which are essential components of the RNA, DNA, and coenzymes that must be synthesized in the proliferation of cancer cells. In the field of oncology, it has long seemed expedient to use purine antagonists as potentially active agents for cancer therapy.

How Do Purine Antagonists Work?

The purine chemical bases (guanine and adenine) are building blocks in the synthesis of DNA and RNA nucleotides. In the cell replication process, nucleotides are joined to one another to create strands of DNA. Exactly how the purine antagonists medications function is unclear; they may inhibit normal production of DNA. It is thought that purine antagonists block DNA synthesis by decreasing the production of the purine bases or else may be incorporated into the DNA strands during synthesis and thus interfere with the process cell replication in cancer. Genetic mutation as seen as a precursor to cancer may lead to purine resistance.


For example, fludarabine or 2-fluoro-ara-amp is an antimetabolite of the purine class. Functioning as a pro-drug, it is dephosphorylated and enters the cancer cell. After that it is rephosphorylated to a chemical called F-ara-ATP. Upon incorporation into the DNA strand, it prevents strand lengthening. The drug is successfully used in treating treatment resistant chronic lymphocytic and chronic B cell leukemias, T-cell lymphoma, and non-Hodgkin’s lymphoma. Another purine agent, 6-Mercaptopurine (6-MP) is is successfully used to traat acute lymphocytic leukemia. Specifically, it works to block the S phase of cell replication. Once it is incorporated into DNA and RNA strands, the nucleic acids become useless. 6-MP also may inhibit synthesis of purine bases. Mercaptopurine (which is one of the many antimetabolite medications tested in the Rxight® panel), is used alone or with other chemotherapy drugs to combat acute lymphocytic leukemia, a type of cancer that starts in the white blood cells (also called ALL, acute lymphatic leukemia and acute lymphoblastic leukemia).

Warnings and Severe Side Effects

Purine antagonists may cause side effects, some of which can be life-threatening. Common side effects of purine antagonists include:

  • Darkening of the skin
  • Hhair loss
  • Rash
  • Nausea
  • Vomiting

    Some side effects can be serious. If you experience any of these symptoms, call your doctor or seek emergency treatment:

  • Unusual bruising or bleeding
  • Yellowing of the skin or eyes (jaundice)
  • Appetite loss
  • Diarrhea
  • Swelling of the stomach area
  • Pain in the upper right part of the stomach
  • Pallor
  • Weakness/fatigue
  • Shortness of breath
  • Sore throat, fever, or other signs of infection
  • Swelling in the legs, ankles, or feet
  • Additionally, treatment with purine antagonists may increase the risk of developing a new form of cancer. Some people who took mercaptopurine to treat Crohn’s disease or ulcerative colitis developed hepatosplenic T cell lymphoma, a very serious type of cancer that usually leads to death within a short time.

    Understand Your Risks with the Rxight® Genetic Test

    Some patients based on their genetics do not process purine antagonists effectively, leading to toxicity and adverse reactions. Others metabolize the drug too quickly, leading to them not deriving benefit at standard doses. Unfortunately, prescribers still rely on the traditional trial-and-error approach in find the optimal dose of a medication for their already physically compromised patient, which can result in the patient experiencing potentially serious side effects or simply not benefiting.


    The advent of pharmacogenetics, the science of how one’s genes affect the ability to process medications, has led to the development of pharmacogenetic testing that leads to tailored pharmacotherapy designed precisely for a patient’s unique genetics. Rxight® pharmacogenetic testing is based in the sequencing of genes involved specifically in the metabolism of medications, and is thus designed to analyze how you might respond to hundreds of OTC and prescription medications across over 50 pharmacological classes, including purine antagonists. In this way, Rxight® serves as a roadmap for current and future prescribers, guiding them in finding a medication dose tailored to the patient’s unique genetics.


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


    Purine Antagonists Tested Include:

    Read more about Rxight® Genetic Testing For Drug Metabolism