Azasan Side Effects

Generic Name: azathioprine

Note: This document contains side effect information about azathioprine. Some of the dosage forms listed on this page may not apply to the brand name Azasan.

Some side effects of Azasan may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

For the Consumer

Applies to azathioprine: oral tablet

Along with its needed effects, azathioprine (the active ingredient contained in Azasan) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking azathioprine:

More common
  • Black, tarry stools
  • bleeding gums
  • blood in the urine or stools
  • chest pain
  • cough or hoarseness
  • fever or chills
  • lower back or side pain
  • painful or difficult urination
  • pinpoint red spots on the skin
  • shortness of breath
  • sore throat
  • sores, ulcers, or white spots on the lips or in the mouth
  • swollen glands
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • Abdominal or stomach pain or tenderness
  • clay-colored stools
  • dark urine
  • decreased appetite
  • fast heartbeat
  • fever (sudden)
  • headaches
  • itching
  • loss of appetite
  • muscle or joint pain
  • nausea, vomiting, and diarrhea (severe)
  • redness or blisters on the skin
  • swelling of the feet or lower legs
  • unusual feeling of discomfort or illness (sudden)
  • yellow eyes or skin
Incidence not known
  • Abdominal or stomach cramps
  • diarrhea
  • difficulty with breathing
  • difficulty with moving
  • fat in the stool
  • general feeling of illness
  • pale skin
  • sores on the skin
  • sudden loss of weight
  • troubled breathing with movement
  • weight loss

Some side effects of azathioprine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common
  • Nausea or vomiting (mild)
  • swollen joints
Incidence not known
  • Hair loss or thinning of the hair

For Healthcare Professionals

Applies to azathioprine: compounding powder, intravenous powder for injection, oral tablet


The principal and potentially serious toxic effects of azathioprine (the active ingredient contained in Azasan) are hematologic and gastrointestinal. Risk of secondary infection and malignancy is also significant. Frequency and severity of side effects depend on dose and duration of azathioprine as well as on underlying disease or concomitant therapies. Hematologic toxicities and neoplasia were reported more often in renal homograft recipients than in patients using azathioprine for rheumatoid arthritis.


Bone marrow suppression is dose related and is the most common cause for dosage reductions.

Leukopenia (any degree) has been reported in greater than 50% of renal homograft recipients and 28% of rheumatoid arthritis patients. Leukopenia (less than 2500/mm3) has been reported in 16% of renal homograft recipients and 5.3% of rheumatoid arthritis patients.

There are data to support an increased risk of bone marrow aplasia in patients with very low or absent thiopurine methyltransferase (TPMT) activity. The majority of the population has high TPMT activity, 11% have moderate activity, and approximately one in 300 persons has very low to no activity. The main metabolic pathway of azathioprine (the active ingredient contained in Azasan) conversion to 6-MP, involves TPMT. Limitations in this pathway lead to increased metabolism via alternate pathways. In patients with low TPMT activity, there is an increase in 6-thioguanine nucleotide (6-TGN) concentrations, a cytotoxic metabolite which suppresses purine synthesis. Despite these findings, bone marrow aplasia has been reported in patients with normal TPMT activity.

A 55-year-old male with pompholyx and deficiency of erythrocyte thiopurine methyltransferase experienced pancytopenia coincident with azathioprine therapy. Ten weeks after starting azathioprine 100 mg per day, a full blood count (during routine monitoring) showed moderate pancytopenia. Azathioprine was discontinued. Ten days later he was admitted to the hospital with malaise, lethargy, and deterioration in blood count. He was treated with blood and platelet transfusions and discharged eight days later with modest improvement in peripheral blood count.

Hematologic side effects have included reversible bone marrow suppression, severe leukopenia, thrombocytopenia, and anemia. Macrocytosis, hemolytic anemia, pure red cell aplasia, and pancytopenia have been reported. Anemias (including macrocytic anemia) and/or bleeding have been reported. Fatal myelosuppression has been reported in a carrier of heterozygous thiopurine S-methyl transferase *1/*3C.


Gastrointestinal side effects tend to be more problematic in the first few months of therapy.

A 20-year-old man developed severe small-bowel villus atrophy and chronic diarrhea after starting azathioprine (the active ingredient contained in Azasan) 50 mg per day. Diarrhea completely resolved within 2 weeks after azathioprine discontinuation. Mucosal biopsies at 4 months post azathioprine discontinuation showed complete reversal of severe duodenal villus atrophy.

Gastrointestinal (GI) side effects have included nausea, vomiting, diarrhea, and anorexia. Severe villus, chronic malabsorption syndrome, acute pancreatitis, GI discomfort, and steatorrhea have been reported. Vomiting with abdominal pain has been reported with hypersensitivity pancreatitis. Case reports of patients with symptoms that imitate viral gastroenteritis (nausea, vomiting, diarrhea, and fever) hours after a single dose of azathioprine have also been reported.


Oncologic side effects have included an increased risk of cancer, particularly lymphomas and leukemias. Case reports of common de novo tumors that have developed in renal transplant patients have included basal cell, squamous cell carcinomas of the skin, urogenital malformations, lung malformations, and Kaposi's sarcoma (cutaneous and visceral). Lymphoproliferative disease in azathioprine-treated rheumatoid arthritis patients have been reported in approximately 1.8 cases per 1000 patient years of follow-up compared to an incidence of 0.8 cases per 1000 patient years of follow-up in the normal population. Epstein-Barr virus-positive lymphoma and hepatosplenic T-cell lymphoma have also been reported.

The increased risk of cancer may be more pronounced when azathioprine is used concomitantly with other immunosuppressive agents.

Renal transplant patients may have a higher risk of developing lymphoproliferative disorders, lymphomas, and leukemia, as well as some solid tumors while receiving azathioprine.

Transplant patients as well as those with rheumatoid arthritis are often treated with multiple immunosuppressants; therefore, the true risk of neoplasia associated with azathioprine alone has yet to be determined.

A small increase in the risk of Epstein-Barr virus-positive lymphoma was seen in a study of patients with inflammatory bowel disease treated with azathioprine.


Other side effects have included infection in up to 20% of patients, even with therapeutic doses of azathioprine (the active ingredient contained in Azasan) These have included fungal, protozoal, viral, and uncommon bacterial infections, some of which have been fatal. Fever, delayed wound healing, oral lesions, fatigue, and malaise have also been reported.


Hepatic side effects have included elevations in alkaline phosphatase, bilirubin, and/or serum transaminases, cholestatic jaundice, hepatitis, and hepatic veno-occlusive disease. Other hepatotoxic side effects have included cirrhosis, perisinusoidal fibrosis, hepatic peliosis, sinusoidal dilatation, cholestasis, and acute focal hepatocellular necrosis. In addition, several cases of nodular regenerative hyperplasia of the liver and at least one case of destructive cholangitis have been reported.

Hepatotoxicity usually occurs within the first six months of therapy and is more common in patients requiring immunosuppression following transplant than in patients requiring therapy for rheumatoid arthritis. Hepatotoxicity, often manifest as cholestasis and/or acute focal hepatocellular necrosis, is generally reversible following discontinuation of azathioprine therapy. However, permanent hepatic damage associated with cirrhosis, perisinusoidal fibrosis, hepatic peliosis, sinusoidal dilatation, and veno-occlusive disease is also reported.

Veno-occlusive disease of the hepatic veins is due to an unknown mechanism, may affect males more often, usually precedes portal hypertension, and carries a poor prognosis. Numerous fatalities have been reported. Permanent discontinuation of azathioprine therapy is indicated if hepatic veno-occlusive disease is suspected.

A 51-year-old man developed jaundice and diffuse abdominal pain two months after the start of azathioprine 1.4 mg/kg/day. Biopsy reports confirmed destruction of the bile ducts consistent with destructive cholangitis. After discontinuation of azathioprine, the abdominal pain disappeared within 2 days; and liver function tests improved and returned to normal values 8 weeks later.


Hypersensitivity side effects have included hypersensitivity rash, leukocytoclastic vasculitis, skin rash, fever, chills, malaise, diarrhea, nausea, hepatitis, hypotension, and circulatory collapse. Hypersensitivity has also been implicated in cases of hepatotoxicity, interstitial nephritis, interstitial pneumonitis, pancreatitis, and vasculitis. As azathioprine (the active ingredient contained in Azasan) is metabolized to 6-mercaptopurine, rechallenge with both agents should be avoided. Hypersensitivity reactions which manifest from mild gastrointestinal disturbances, fever, and myalgias to severe hypotension and shock have been reported. Rhabdomyolysis has been reported as part of an azathioprine hypersensitivity syndrome. At least 3 cases of erythema nodosum, 2 cases of pustules, and 1 case of contact dermatitis have been reported.

Erythema nodosum and pustules are rarely reported manifestations of azathioprine hypersensitivity. Both types of skin lesions may be related to the clinical activity of inflammatory bowel disease. Relapse of such lesions shortly after rechallenge should raise the hypothesis of hypersensitivity rather than pharmacological manifestations.

Gastrointestinal hypersensitivity is characterized by severe nausea and vomiting which may be accompanied by diarrhea, rash, fever, malaise, myalgias, elevated liver function tests, and hypotension.


A 52-year-old male with steroid-dependent ulcerative colitis experienced atrial fibrillation coincident with azathioprine (the active ingredient contained in Azasan) therapy. The drug had been started 3 years earlier, but discontinued after a few months because the patient reported palpitations, lipothymia, nausea, and vomiting. Upon a rechallenge with 50 mg of azathioprine, the patient showed general malaise, nausea, and vomiting. An ECG showed atrial fibrillation, and the patient reported that the symptoms were similar to those experienced previously.

Azathioprine-induced hypotension is independent of dose and may accompany signs and symptoms of hypersensitivity. Hypotension may be profound, although it is usually responsive to intravenous fluids and, if hypersensitivity is suspected, corticosteroids.

Cardiovascular side effects have included rare cases of hypotension, including cardiogenic shock. At least three cases of atrial fibrillation have been reported (one case involving a patient with ulcerative colitis), although causality is unknown.


Respiratory side effects have included reversible interstitial pneumonitis. Interstitial pneumonitis associated with a restrictive pattern on pulmonary function tests has been reported.

Review of seven rare cases of azathioprine-associated interstitial pneumonitis revealed that the progression from alveolitis to pulmonary fibrosis may be dose-related.


A reduction in the incidence of chronic allograft nephropathy has been reported during the extended follow-up (greater than or equal to 10 years) of patients (n=128) participating in a randomized trial that examined the conversion from cyclosporine to azathioprine (the active ingredient contained in Azasan) as early as three months after renal transplantation.

A 47-year-old female with Wegener's granulomatosis experienced rapid progression of renal failure within 10 days of starting azathioprine for vasculitis. Her creatinine was 119 mcmol/L at the time of presentation. Acute tubulointerstitial nephritis and no active glomerulonephritis were observed on renal biopsy. Her renal function started improving by day 6 post-admission and at one month post-admission her serum creatinine was 116 mcmol/L. She continued to have reasonable renal function and 16 months later had creatinine of 104 mcmol/L with no clinical evidence of recurrent interstitial nephritis.

Renal side effects have included elevation in serum creatinine and BUN accompanied by oliguria, but are usually associated with hypotension, and normalize after treatment with intravenous hydration and steroids. Rare cases of hematuria secondary to azathioprine-induced crystalluria have been reported, and may be less common with high urine output. Chronic allograft nephropathy and at least one case of acute interstitial nephritis have been reported.


Dermatologic side effects have included skin rashes, alopecia, verrucae, zoster, increased skin color, malignant neoplasms, Kaposi sarcoma, dermatomycoses, cytomegalovirus infection, scabies, skin lesions, Sweet's syndrome (acute febrile neutrophilic dermatosis), and at least one case of skin peeling syndrome.

A female patient developed skin peeling syndrome eight months after the dosage of azathioprine was reduced to 25 mg daily. Skin lesions resolved 30 days after drug withdrawal.

Excess sun exposure, pale skin types, and duration of allograft seem to be important risk factors in the development of skin lesions.


Immunologic side effects have included at least one case of bilateral cytomegalovirus (CMV) retinitis.

A patient with systemic lupus erythematosus and end-stage renal disease experienced CMV retinitis coincident with azathioprine therapy. It is theorized that immunosuppressive therapy may have a role in the development of CMV retinitis in this population. The patient responded to discontinuation of azathioprine, lowering of the corticosteroid dose, and systemic administration of ganciclovir.


Metabolic side effects have included negative nitrogen balance.


Musculoskeletal side effects have included arthralgias.

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