Azathioprine

Kidney Transplant Rejection Prevention

Azathioprine is used to help prevent the body from rejecting a newly transplanted kidney. It works by weakening the immune system so it does not attack the donor organ. It is typically prescribed as an adjunct therapy, meaning it is used in combination with other medications, such as corticosteroids, to ensure the transplant is successful.

Rheumatoid Arthritis

This medication is also used to manage the symptoms of severe, active rheumatoid arthritis in adults. It is generally reserved for patients who have not responded well to other standard treatments, such as rest, physical therapy, or nonsteroidal anti-inflammatory drugs (NSAIDs). When used for this condition, azathioprine can help to:

• Reduce joint pain and swelling.
• Decrease joint stiffness.
• Improve overall physical function and mobility.

Because it affects the immune system, healthcare providers monitor patients closely while they are taking this medication for these conditions.

Immune System Regulation

Azathioprine belongs to a class of drugs known as immunosuppressants. Its primary function is to lower the body's natural defense system (the immune response). This is necessary when the immune system is overactive or when it might attack a foreign object, such as a transplanted organ.

How It Affects Cells

The medication works by interfering with the production of DNA and RNA, which are the building blocks cells need to grow and divide. It specifically targets cells that multiply rapidly, such as the white blood cells in the immune system. By slowing down the production of these cells, azathioprine helps to:

• Stop the immune system from attacking and rejecting a transplanted kidney.
• Reduce the inflammation, pain, and swelling associated with autoimmune conditions like rheumatoid arthritis.

In the body, azathioprine is converted into an active substance that blocks the metabolism of purines, which are essential for creating new genetic material in cells. This process helps keep the immune response under control and prevents it from causing damage to the body.

Common Side Effects

Some people may experience mild side effects when starting azathioprine. These often include:

• Nausea and vomiting
• Diarrhea
• Loss of appetite
• Stomach pain
• Temporary hair thinning or loss
• Skin rash

Serious Side Effects

Azathioprine can suppress the immune system, which may lead to serious health concerns. Seek medical attention immediately if you experience:

• Signs of infection, such as fever, chills, sore throat, or persistent cough
• Unusual bruising or bleeding
• Extreme tiredness or weakness
• Pale skin
• Yellowing of the eyes or skin (jaundice)
• Dark-colored urine
• Severe pain in the upper stomach that may spread to the back
• Muscle or joint pain
• Shortness of breath

Long-term use of this medication may increase the risk of developing certain types of cancer, such as lymphoma or skin cancer. It is important to report any new skin growths or changes in moles to a healthcare provider.

Boxed Warning: Risk of Cancer

Azathioprine is associated with an increased risk of developing malignancies, particularly lymphoma and skin cancers. This risk is higher for individuals who take the medication for long periods or in combination with other immunosuppressants. A rare and often fatal type of cancer called hepatosplenic T-cell lymphoma has been reported, primarily in young men with inflammatory bowel disease who were also taking certain other medications.

Infection Risk

Because this medication suppresses the immune system, it increases the risk of serious bacterial, viral, fungal, and protozoal infections. These infections can be severe or even fatal. There have also been reports of progressive multifocal leukoencephalopathy (PML), a rare and serious brain infection, in people taking this drug.

Bone Marrow Suppression

Azathioprine can cause a significant drop in blood cell counts, including white blood cells, red blood cells, and platelets. This can lead to anemia, an increased risk of bleeding, or a higher chance of infection. Regular blood tests are necessary to monitor these levels, as the suppression is often related to the dosage used.

Genetic Factors and Toxicity

Some individuals have a genetic deficiency in enzymes called TPMT or NUDT15. People with these deficiencies are at a much higher risk for severe, life-threatening bone marrow toxicity when taking azathioprine. Testing for these genetic variations may be considered before starting treatment to help determine a safe dose.

Liver Health

This medication can cause liver damage (hepatotoxicity). Healthcare providers typically monitor liver function tests regularly to detect early signs of liver issues, which may require stopping the medication.

Pregnancy and Breastfeeding

Azathioprine can cause fetal harm when administered to pregnant women. It is generally not recommended during pregnancy unless the potential benefits outweigh the risks. Effective contraception is usually advised for both men and women during treatment. Breastfeeding is typically discouraged while using this medication as it may pass into breast milk.

Pregnancy Considerations

Azathioprine can cause harm to an unborn baby. Clinical data has shown that the use of this medication during pregnancy is associated with an increased risk of certain complications, such as:

• Preterm delivery
• Lower than average birth weight
• Potential for physical birth defects

Healthcare providers generally recommend that individuals who can become pregnant use effective birth control while taking azathioprine. If you are planning a pregnancy or become pregnant while on this medication, contact your doctor to discuss the risks and benefits of continuing treatment.

Breastfeeding Considerations

Azathioprine and its metabolites have been detected in breast milk. There is a risk that the medication could cause serious side effects in a nursing infant. Because of these potential risks, it is usually recommended to either discontinue breastfeeding or stop taking the medication. Patients should consult with their healthcare team to determine the safest course of action based on their specific medical needs.

Available Forms

Azathioprine is produced in the following forms:

• Oral Tablet: This is the most common form of the medication taken by mouth.
• Injection: A powder for reconstitution is available for intravenous administration. This form is typically used in a clinical setting when a patient cannot take the medication orally.

FDA Approval and Indications

Azathioprine is approved by the U.S. Food and Drug Administration (FDA) for two primary indications. It is used as an adjunct for the prevention of rejection in renal (kidney) homotransplantation. It is also indicated for the management of severe, active, erosive rheumatoid arthritis in adults who have not responded to conventional treatments like rest, nonsteroidal anti-inflammatory drugs (NSAIDs), or other disease-modifying antirheumatic drugs (DMARDs).

Boxed Warning

The FDA has issued a Boxed Warning for azathioprine because chronic immunosuppression with this drug increases the risk of malignancy in humans. Reports of post-transplant lymphoma and hepatosplenic T-cell lymphoma (HSTCL) have been documented, particularly in patients with inflammatory bowel disease. Physicians are required to inform patients of the risk of cancer and monitor them for any signs of new growths or unusual symptoms.

Regulatory Status

• Prescription Requirement: This medication is available by prescription only.
• Controlled Substance: Azathioprine is not a controlled substance.

Although azathioprine is frequently used to treat other autoimmune conditions, such as Crohn's disease or systemic lupus erythematosus, these uses may not be specifically listed in the FDA-approved labeling for all formulations.

Risks to the Fetus

Azathioprine is known to cause fetal harm when taken during pregnancy. The medication can cross the placenta, and clinical evidence suggests that exposure may increase the risk of birth defects or other developmental issues. It is typically only prescribed during pregnancy if the mother's health condition is serious and no safer alternative is available.

Newborn Health Concerns

Infants born to individuals who used azathioprine during pregnancy may experience certain blood-related complications at birth. These potential issues include:

• Leukopenia: A decrease in white blood cells, which can make it harder for the infant to fight infections.
• Thrombocytopenia: A decrease in platelets, which are necessary for proper blood clotting.
• Immune Suppression: A general reduction in the infant's immune system function.

Pregnancy Prevention and Planning

Due to the risks of fetal harm, healthcare providers recommend the following precautions:

• Contraception: Individuals of childbearing potential should use effective birth control while taking azathioprine. Some guidelines suggest continuing birth control for a specific period after the final dose.
• Testing: A pregnancy test may be required before starting the medication to ensure the patient is not pregnant.
• Consultation: If you are planning a pregnancy or discover you are pregnant while taking this medication, contact your healthcare provider immediately. They will evaluate the risks to the fetus against the risks of leaving the mother's condition untreated.