Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
AZASAN vs ENVARSUS XR
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Azathioprine is a purine analog that inhibits purine synthesis, thereby interfering with DNA and RNA synthesis. It is metabolized to 6-mercaptopurine, which inhibits T-cell activation and proliferation, leading to immunosuppression.
Calcineurin inhibitor. Binds to FKBP-12, forming a complex that inhibits calcineurin phosphatase, thereby blocking T-cell activation and IL-2 transcription.
Renal transplant rejection prophylaxis,Rheumatoid arthritis,Off-label: inflammatory bowel disease (Crohn's disease, ulcerative colitis), lupus nephritis, autoimmune hepatitis, pemphigus vulgaris, myasthenia gravis, Behçet's disease, dermatomyositis, polymyositis
Prophylaxis of organ rejection in kidney transplant patients,Prophylaxis of organ rejection in liver transplant patients
1-3 mg/kg/day orally once daily or divided twice daily; maximum dose 2.5 mg/kg/day for rheumatoid arthritis; usual dose 50-150 mg/day.
0.2 mg/kg/day orally once daily, with the morning meal, using extended-release tablets. Dose adjustments guided by trough concentrations.
Terminal elimination half-life of azathioprine is approximately 4.5 hours (range 2–6 h), while its active metabolite 6-mercaptopurine has a half-life of 0.5–2 hours. Clinical context: Renal impairment prolongs half-life.
Terminal half-life approximately 25-30 hours in stable renal transplant patients. Longer half-life (up to 50 hours) in patients with hepatic impairment.
Metabolized via xanthine oxidase and thiopurine methyltransferase (TPMT) to active and inactive metabolites. Co-administration with allopurinol inhibits xanthine oxidase, requiring dose reduction of azathioprine.
Primarily hepatic via CYP3A4 and CYP3A5; also metabolized by intestinal CYP3A4.
Renal: 88% as 6-mercaptopurine and metabolites; biliary: <10%
Primarily fecal (94%) with minor renal excretion (2.2% as unchanged drug). Biliary excretion is a significant route.
30% bound to plasma proteins, primarily albumin.
Approximately 99% bound to erythrocytes and plasma proteins, primarily albumin and alpha-1-acid glycoprotein.
0.8–1.0 L/kg, indicating extensive distribution into tissues.
0.9-1.4 L/kg in renal transplant patients; large volume indicates extensive tissue distribution, particularly to red blood cells.
Oral: 41–47% (azathioprine); 100% for IV administration.
Oral bioavailability is approximately 15-25% with the extended-release formulation; reduced by high-fat meal, so should be taken consistently on an empty stomach.
GFR >50 m L/min: no adjustment; GFR 10-50 m L/min: 75% of normal dose; GFR <10 m L/min: 50% of normal dose.
No specific GFR-based dose adjustment; however, due to nephrotoxicity, monitor renal function closely and reduce dose if renal impairment occurs. For patients with severe renal impairment (Cr Cl <30 m L/min), consider alternative immunosuppression.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: contraindicated.
In patients with mild to moderate hepatic impairment (Child-Pugh A or B), reduce dose by 25%. For severe hepatic impairment (Child-Pugh C), reduce dose by 50% and monitor trough levels closely.
2-3 mg/kg/day orally once daily; initial dose 1 mg/kg/day in divided doses; not recommended in children <1 year.
For pediatric kidney transplant recipients: 0.2 mg/kg/day orally once daily, with morning meal. Adjust to target trough concentrations. Safety and efficacy not established for other indications in pediatrics.
Start at low end of dosing range (50 mg once daily); monitor renal function and adjust accordingly.
No specific dose adjustment; however, elderly patients may have increased susceptibility to nephrotoxicity and neurotoxicity. Use lowest effective dose, monitor renal function, and adjust based on trough levels.
Chronic immunosuppression increases the risk of malignancy, particularly lymphoma and skin cancer. Patients should be monitored for neoplasia. The drug should be used only if potential benefits outweigh risks.
Increased susceptibility to infection and possible development of malignancy (e.g., lymphoma, skin cancer).
Hematologic toxicity (leukopenia, thrombocytopenia, anemia) - monitor blood counts. Hepatotoxicity. Increased infection risk. Hypersensitivity reactions. TPMT deficiency increases toxicity risk. Monitor for pancreatitis, especially in Crohn's patients. Avoid live vaccines. Photosensitivity and skin cancer risk.
Nephrotoxicity, neurotoxicity, hypertension, hyperkalemia, post-transplant diabetes mellitus, monitoring of blood concentrations required.
Hypersensitivity to azathioprine or 6-mercaptopurine. Pregnancy (category D) unless potential benefit justifies risk. Lactation. Severe hepatic impairment. Myelosuppression or active infection. Concurrent use with allopurinol without dose adjustment.
Hypersensitivity to tacrolimus or any component of the formulation.
No significant food interactions. May be taken with food to reduce gastrointestinal upset. Avoid concurrent use with raw or undercooked meats to reduce risk of infection due to immunosuppression.
Grapefruit and grapefruit juice increase tacrolimus exposure and must be avoided. High-fat meals may decrease absorption; consistency of food intake relative to dosing is recommended. Alcohol should be limited due to potential additive hepatotoxicity.
Azathioprine is FDA Pregnancy Category D. First trimester: Associated with congenital anomalies (e.g., atrial septal defect, limb defects) in case reports, but risk may be lower than with other immunosuppressants. Second and third trimesters: Risk of fetal growth restriction, preterm delivery, and neonatal immunosuppression. Avoid unless benefit outweighs risk.
Envarsus XR (tacrolimus) is classified as FDA Pregnancy Category C. In the first trimester, there is an increased risk of congenital anomalies (e.g., cardiac, renal) based on animal studies; human data are limited but suggest a possible small increase. During the second and third trimesters, risks include intrauterine growth restriction, preterm delivery, and transient neonatal hyperkalemia and renal dysfunction. Advise women of childbearing potential to use effective contraception.
Azathioprine is excreted into breast milk in small amounts; milk-to-plasma ratio approximately 0.1. Infant exposure is low, but theoretical risk of immunosuppression. Weigh benefits against risks; consider monitoring infant for leukopenia and infections.
Tacrolimus is excreted into human breast milk. The milk-to-plasma ratio is approximately 0.5 (range 0.12–0.75). Infant exposure is estimated to be <1% of the maternal weight-adjusted dose, which is considered low. However, due to potential for immunosuppression and adverse effects, breastfeeding is generally not recommended unless benefits outweigh risks. Monitor infant for signs of immunosuppression.
Increased clearance and reduced bioavailability during pregnancy may require dose increase to maintain therapeutic levels; monitor thiopurine metabolite levels (6-TGN, 6-MMP) and adjust accordingly. Often no change required if stable disease.
Pregnancy induces pharmacokinetic changes including increased volume of distribution, altered protein binding, and enhanced clearance of tacrolimus. Frequent monitoring of trough concentrations is essential to maintain therapeutic levels (target 5–10 ng/m L). Dose adjustments (increases of 20–50% or more) are often required, especially during the second and third trimesters. Postpartum, doses should be reduced to pre-pregnancy levels within 1–2 weeks.
Azasan (azathioprine) is a prodrug of 6-mercaptopurine. Screen for TPMT deficiency before initiation to avoid severe myelosuppression. Monitor CBC and liver function weekly for first month, then monthly. Corticosteroid-sparing agent in autoimmune conditions. Avoid live vaccines during therapy.
ENVARSUS XR is an extended-release formulation of tacrolimus; conversion from immediate-release tacrolimus requires close therapeutic drug monitoring due to altered pharmacokinetics. Administer consistently with or without food to minimize variability. Avoid grapefruit products. Monitor renal function, blood pressure, electrolytes, glucose, and trough tacrolimus levels. CYP3A4/5 inducers/inhibitors significantly affect tacrolimus exposure; adjust dose accordingly. Do not crush, chew, or split tablets.
Take exactly as prescribed; do not change dose without consulting your doctor.,Report any signs of infection, unusual bruising/bleeding, or fatigue immediately.,Avoid exposure to individuals with infections; maintain good hand hygiene.,Use effective contraception during treatment and for at least 3 months after stopping.,Do not receive live vaccines (e.g., MMR, varicella) while taking this medication.,Limit sun exposure; use sunscreen and protective clothing due to increased skin cancer risk.
Take exactly as prescribed, at the same time each day, with or without food but consistently.,Swallow whole; do not crush, chew, or break the tablet.,Avoid grapefruit and grapefruit juice.,Do not stop or change dose without consulting your doctor.,Report signs of infection (fever, sore throat), tremor, headache, changes in urination, or unusual bleeding.,Avoid live vaccines and limit sun exposure due to increased skin cancer risk.,Keep all appointments for blood tests to monitor drug levels and organ function.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about AZASAN vs ENVARSUS XR, answered by our medical review team.
AZASAN is a Immunosuppressant that works by Azathioprine is a purine analog that inhibits purine synthesis, thereby interfering with DNA and RNA synthesis. It is metabolized to 6-mercaptopurine, which inhibits T-cell activation and proliferation, leading to immunosuppression.. ENVARSUS XR is a Calcineurin Inhibitor Immunosuppressant that works by Calcineurin inhibitor. Binds to FKBP-12, forming a complex that inhibits calcineurin phosphatase, thereby blocking T-cell activation and IL-2 transcription.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between AZASAN and ENVARSUS XR depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of AZASAN is: 1-3 mg/kg/day orally once daily or divided twice daily; maximum dose 2.5 mg/kg/day for rheumatoid arthritis; usual dose 50-150 mg/day.. The standard adult dose of ENVARSUS XR is: 0.2 mg/kg/day orally once daily, with the morning meal, using extended-release tablets. Dose adjustments guided by trough concentrations.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between AZASAN and ENVARSUS XR in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. AZASAN is classified as Category C. Azathioprine is FDA Pregnancy Category D. First trimester: Associated with congenital anomalies (e.g., atrial septal defect, limb defects) in case reports, but risk may be lower th. ENVARSUS XR is classified as Category C. Envarsus XR (tacrolimus) is classified as FDA Pregnancy Category C. In the first trimester, there is an increased risk of congenital anomalies (e.g., cardiac, renal) based on anima. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.