Imuran: Immunosuppressive Precision for Autoimmune & Transplant Management
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Synonyms | |||
Imuran (azathioprine) is a cornerstone immunosuppressive agent with over five decades of clinical evidence supporting its use in transplant medicine and autoimmune disorders. As a purine analogue antimetabolite, it exerts its therapeutic effects by selectively inhibiting purine synthesis, thereby suppressing rapid cellular proliferation—particularly in immunologically active cells. This mechanism provides a calibrated approach to modulating overactive immune responses without complete immunosuppression. It is available in oral tablet and intravenous formulations, though oral administration is standard for chronic management. Imuran is typically considered a maintenance therapy, often used in combination with other immunosuppressants like corticosteroids to allow for lower dosing of each agent and reduce cumulative toxicity. Its well-established pharmacokinetic profile allows for predictable dosing, though therapeutic drug monitoring and regular blood tests are essential due to its narrow therapeutic index and potential for hematologic toxicity.
Features
- Active ingredient: Azathioprine
- Available formulations: 25 mg, 50 mg, and 75 mg oral tablets; lyophilized powder for IV injection
- Mechanism of action: Purine analogue antimetabolite; inhibits DNA, RNA, and protein synthesis
- Bioavailability: Approximately 47% oral bioavailability with significant interpatient variability
- Metabolism: Hepatic conversion to active metabolites (6-mercaptopurine and thioguanine nucleotides)
- Half-life: Approximately 5 hours for azathioprine; active metabolites have longer half-lives
- Excretion: Primarily renal (elimination of metabolites)
- Pregnancy category: D (evidence of human fetal risk)
Benefits
- Reduces risk of acute organ rejection in renal, cardiac, and hepatic transplantation
- Enables corticosteroid dose reduction, minimizing long-term steroid-related adverse effects
- Provides sustained control of autoimmune disease activity in conditions like rheumatoid arthritis and lupus
- Offers oral dosing convenience for long-term outpatient management
- Well-established safety profile with decades of real-world clinical experience
- Cost-effective compared to newer biologic immunosuppressants
Common use
Imuran is FDA-approved for prevention of rejection in renal transplantation and management of severe, active rheumatoid arthritis unresponsive to conventional treatments. It is widely used off-label for various autoimmune conditions including systemic lupus erythematosus, autoimmune hepatitis, inflammatory bowel disease (Crohn’s disease and ulcerative colitis), myasthenia gravis, and certain vasculitides. In transplant settings, it is typically initiated perioperatively and continued indefinitely as maintenance immunosuppression. For autoimmune conditions, it is generally reserved for cases where first-line therapies have proven inadequate or poorly tolerated. The medication requires 6-8 weeks to demonstrate full therapeutic effect, making it unsuitable for acute disease flares.
Dosage and direction
Dosing is weight-based and indication-specific. For transplant rejection prevention: Initial dose is 3-5 mg/kg/day orally, usually beginning on the day of transplantation or 1-3 days prior. Maintenance doses are typically reduced to 1-3 mg/kg/day. For rheumatoid arthritis: Initial dose is 1 mg/kg/day (50-100 mg) as a single dose or divided twice daily. Dose may be increased by 0.5 mg/kg/day after 6-8 weeks if response is insufficient and no toxicity observed. Maximum dose is 2.5 mg/kg/day. Tablets should be taken with food to minimize gastrointestinal upset. Dosage adjustments are required in patients with renal impairment or those taking allopurinol (dose reduction of 65-75% recommended). Regular complete blood counts must be monitored, especially during initial treatment and after dosage changes.
Precautions
Imuran requires careful hematologic monitoring due to its myelosuppressive effects. Complete blood counts should be obtained weekly during the first month, twice monthly for the second and third months, then monthly thereafter. Liver function tests should be monitored regularly. Patients should be advised to report any signs of infection, unusual bleeding, bruising, or fatigue promptly. Vaccination with live vaccines is contraindicated during treatment. Due to immunosuppression, patients have increased susceptibility to infections and possible increased risk of neoplasia, particularly skin cancers—regular dermatologic examinations are recommended. Patients should use sun protection measures diligently. Imuran is mutagenic and poses potential reproductive risks; appropriate contraception is essential during treatment.
Contraindications
Imuran is contraindicated in patients with known hypersensitivity to azathioprine or any component of the formulation. It should not be used in patients who have previously exhibited severe hematologic toxicity to azathioprine, mercaptopurine, or thioguanine. Absolute contraindications include pregnancy (unless potential benefit justifies potential fetal risk), and patients with absent thiopurine methyltransferase (TPMT) activity (homozygous deficient). Concomitant use with live vaccines is contraindicated. Relative contraindications include active infection, significantly impaired hepatic or renal function, and concurrent use with other potent myelosuppressive agents.
Possible side effect
Common side effects (≥10%): Nausea, vomiting, diarrhea, leukopenia, thrombocytopenia, anemia, rash, fever. Less common (1-10%): Hepatotoxicity (elevated transaminases), pancreatitis, alopecia, arthralgia, stomatitis. Rare (<1%): Severe bone marrow suppression, opportunistic infections, lymphoma and other malignancies, pneumonitis, Stevens-Johnson syndrome. Gastrointestinal symptoms often diminish with continued use or dose reduction. Myelosuppression is dose-related and usually reversible with dose adjustment or temporary discontinuation. Pancreatitis typically presents with abdominal pain and nausea and requires immediate discontinuation.
Drug interaction
Significant interactions occur with allopurinol, febuxostat, and other xanthine oxidase inhibitors which decrease azathioprine metabolism, increasing toxicity risk—dose reduction of 65-75% is mandatory. Warfarin effect may be reduced due to decreased prothrombin time. ACE inhibitors may increase leukopenia risk. Other myelosuppressive agents (including sulfasalazine, methotrexate) increase hematologic toxicity potential. Live vaccines may have reduced efficacy and increased adverse reaction risk. Aminosalicylate derivatives (olsalazine, mesalamine) may inhibit TPMT, increasing toxicity risk.
Missed dose
If a dose is missed, it should be taken as soon as remembered unless it is nearly time for the next dose. In that case, the missed dose should be skipped and the regular dosing schedule resumed. Patients should not double the dose to make up for a missed dose. Consistent daily administration is important for maintaining stable immunosuppression, particularly in transplant patients. If multiple doses are missed, patients should contact their healthcare provider for guidance, as additional monitoring may be required.
Overdose
Azathioprine overdose primarily manifests as hematologic toxicity including leukopenia, thrombocytopenia, and anemia, which may be severe and prolonged. Nausea, vomiting, diarrhea, and liver enzyme elevations may occur. Management is supportive and includes immediate discontinuation of the drug, hospitalization for monitoring of blood counts, and transfusion support if indicated. Hemodialysis is not effective due to high protein binding and extensive metabolism. There is no specific antidote. Granulocyte colony-stimulating factor may be considered for severe leukopenia. Complete recovery may take several weeks due to the drug’s mechanism of action.
Storage
Store at controlled room temperature (20-25°C or 68-77°F) in the original container with the lid tightly closed. Protect from light and moisture. Do not store in bathroom or kitchen where humidity and temperature variations may occur. Keep out of reach of children and pets. Do not use if tablets show signs of discoloration or deterioration. Properly discard any unused medication after the expiration date or when treatment is discontinued.
Disclaimer
This information is for educational purposes only and does not constitute medical advice. Imuran is a prescription medication that should only be used under the supervision of a qualified healthcare provider familiar with immunosuppressive therapy. Individual patient response and appropriate dosing may vary based on clinical status, concomitant medications, and genetic factors including TPMT status. Patients should not initiate, adjust, or discontinue this medication without consulting their physician. The full prescribing information should be consulted before administration.
Reviews
Clinical studies demonstrate Imuran’s efficacy in transplant rejection prevention, with one-year graft survival rates exceeding 85% when used in combination regimens. In rheumatoid arthritis, approximately 65-70% of patients show significant improvement in disease activity measures. Many clinicians appreciate its predictable pharmacokinetics and decades of real-world experience, though most note the necessity of vigilant monitoring. Patient reviews frequently mention gastrointestinal side effects as an initial challenge that often improves with time, with many reporting satisfactory long-term disease control. The requirement for regular blood tests is commonly cited as a treatment burden.