Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ENVARSUS XR vs AZATHIOPRINE SODIUM
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Calcineurin inhibitor. Binds to FKBP-12, forming a complex that inhibits calcineurin phosphatase, thereby blocking T-cell activation and IL-2 transcription.
Azathioprine is a prodrug of 6-mercaptopurine. It inhibits purine synthesis by interfering with the synthesis of DNA, RNA, and cellular proteins, thereby suppressing immune responses.
Prophylaxis of organ rejection in kidney transplant patients,Prophylaxis of organ rejection in liver transplant patients
Renal transplantation (adjunctive immunosuppression),Rheumatoid arthritis (active, severe, not responsive to conventional therapy),Off-label: Inflammatory bowel disease (Crohn's disease, ulcerative colitis), autoimmune hepatitis, systemic lupus erythematosus, vasculitis, myasthenia gravis, pemphigus vulgaris
0.2 mg/kg/day orally once daily, with the morning meal, using extended-release tablets. Dose adjustments guided by trough concentrations.
1-2 mg/kg/day IV or oral, initially; maintenance 0.5-1 mg/kg/day IV or oral. For severe organ rejection: 3-5 mg/kg/day IV.
Terminal half-life approximately 25-30 hours in stable renal transplant patients. Longer half-life (up to 50 hours) in patients with hepatic impairment.
Terminal elimination half-life of azathioprine is approximately 3-5 hours; its active metabolite 6-mercaptopurine has a half-life of 0.5-1.5 hours. However, the pharmacodynamic effect (immunosuppression) persists longer due to intracellular accumulation of thioguanine nucleotides.
Primarily hepatic via CYP3A4 and CYP3A5; also metabolized by intestinal CYP3A4.
Primarily metabolized by xanthine oxidase (XO) and thiopurine methyltransferase (TPMT) to active and inactive metabolites. Also metabolized by aldehyde oxidase and glutathione S-transferase. Concomitant use with allopurinol (XO inhibitor) requires dose reduction.
Primarily fecal (94%) with minor renal excretion (2.2% as unchanged drug). Biliary excretion is a significant route.
Primarily renal: approximately 50% as unchanged drug and metabolites (6-mercaptopurine, thiouric acid) within 24 hours. Biliary/fecal excretion accounts for minor fraction (<5%).
Approximately 99% bound to erythrocytes and plasma proteins, primarily albumin and alpha-1-acid glycoprotein.
Approximately 30% bound to serum proteins, primarily albumin.
0.9-1.4 L/kg in renal transplant patients; large volume indicates extensive tissue distribution, particularly to red blood cells.
Apparent volume of distribution is 0.6-1.0 L/kg, indicating distribution into total body water and tissues.
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.
Oral bioavailability of azathioprine is approximately 60-70% (range 27-82%) due to first-pass metabolism. Intravenous administration yields 100% bioavailability.
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.
GFR 50-80 m L/min: no adjustment. GFR 30-50 m L/min: reduce dose by 25% to 50%. GFR 10-30 m L/min: reduce dose by 50% to 75%. GFR <10 m L/min: avoid or use with extreme caution.
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.
Child-Pugh class A: no adjustment. Child-Pugh class B: reduce dose by 50%. Child-Pugh class C: avoid use.
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.
2-5 mg/kg/day IV or oral, divided every 12-24 hours; dose based on body weight (mg/kg).
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.
Start at lower end of dosing range; monitor renal function and adjust accordingly. Consider reduced initial dose (e.g., 1 mg/kg/day) due to age-related decreased renal function.
Increased susceptibility to infection and possible development of malignancy (e.g., lymphoma, skin cancer).
MALIGNANCY: Immunosuppression increases risk of lymphoma and other malignancies, particularly skin cancers. Monitor for neoplasia, especially in renal transplant patients.
Nephrotoxicity, neurotoxicity, hypertension, hyperkalemia, post-transplant diabetes mellitus, monitoring of blood concentrations required.
Hematotoxicity (leukopenia, thrombocytopenia, anemia) - monitor CBC. Hepatotoxicity - monitor liver function tests. Increased infection risk. Pancreatitis. Hypersensitivity reactions. Increased risk of malignancy (skin cancer, lymphoma). Use with caution in renal/hepatic impairment. Test for TPMT deficiency before use.
Hypersensitivity to tacrolimus or any component of the formulation.
Hypersensitivity to azathioprine or 6-mercaptopurine. Severe active infection. Pregnancy (FDA Category D), especially first trimester. Lactation. Concomitant use with allopurinol (unless dose adjusted). TPMT deficiency (increased risk of severe myelotoxicity).
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.
Avoid raw or undercooked meats and fish to reduce infection risk; no specific dietary restrictions; grapefruit juice has no known interaction.
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.
FDA Category D. Hematologic toxicity and immunosuppression in the neonate. Increased risk of congenital malformations (cleft palate, skeletal anomalies) and fetal growth restriction. First trimester exposure associated with highest risk; second and third trimester risks include intrauterine growth restriction and preterm birth.
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.
Contraindicated during breastfeeding due to potential immunosuppression and hematologic toxicity in the nursing infant. M/P ratio: Not established.
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.
Azathioprine dose may need to be reduced due to increased clearance in pregnancy; monitor 6-thioguanine nucleotide levels. Empiric dose adjustments not standardized; titrate to maintain therapeutic effect while minimizing myelotoxicity.
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.
Monitor CBC and LFTs weekly for first month, then biweekly for next 2 months, then monthly; dose reduction required with allopurinol coadministration (reduce to 25% of usual dose); screen for TPMT and NUDT15 deficiency before initiating therapy; avoid live vaccines; increased risk of lymphoproliferative disorders; use sun protection due to photosensitivity; pregnancy category D.
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.
Take exactly as prescribed, do not stop without consulting your doctor.,Report any signs of infection (fever, sore throat, easy bruising or bleeding) immediately.,Use effective contraception during treatment and for at least 3 months after stopping.,Avoid live vaccines (e.g., MMR, varicella, nasal flu) while on this medication.,Limit sun exposure and use broad-spectrum sunscreen and protective clothing.,Do not take allopurinol without your doctor's knowledge.,Attend all scheduled blood tests to monitor for side effects.,May cause nausea; take with food if upset stomach occurs.
No interactions on record
"Azathioprine may reduce the therapeutic efficacy and cardiotoxic effects of digitoxin by accelerating its metabolism through induction of cytochrome P450 enzymes, particularly CYP3A4. This interaction can lead to decreased digitoxin serum concentrations, potentially resulting in loss of heart rate control in patients with atrial fibrillation or heart failure. Conversely, the cardiotoxic risk of digitoxin is diminished, but the therapeutic goal may be compromised."
"Azathioprine and fingolimod both suppress lymphocyte function, leading to additive or synergistic immunosuppression. This combination increases the risk of severe infections, including opportunistic infections, due to profound immune system suppression. Clinically, patients may present with prolonged lymphopenia, increased susceptibility to infections, and potential reactivation of latent viruses such as JC virus (causing progressive multifocal leukoencephalopathy) or cytomegalovirus."
"Azathioprine, an immunosuppressant that acts as a prodrug for 6-mercaptopurine, can increase the myelosuppressive effects of benazepril, an ACE inhibitor. This interaction is likely due to additive bone marrow suppression, leading to an elevated risk of leukopenia, anemia, and thrombocytopenia, especially in patients with renal impairment or concomitant use of other myelosuppressive agents."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ENVARSUS XR vs AZATHIOPRINE SODIUM, answered by our medical review team.
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.. AZATHIOPRINE SODIUM is a Immunosuppressant that works by Azathioprine is a prodrug of 6-mercaptopurine. It inhibits purine synthesis by interfering with the synthesis of DNA, RNA, and cellular proteins, thereby suppressing immune responses.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ENVARSUS XR and AZATHIOPRINE SODIUM 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 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.. The standard adult dose of AZATHIOPRINE SODIUM is: 1-2 mg/kg/day IV or oral, initially; maintenance 0.5-1 mg/kg/day IV or oral. For severe organ rejection: 3-5 mg/kg/day IV.. 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 ENVARSUS XR and AZATHIOPRINE SODIUM 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. 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. AZATHIOPRINE SODIUM is classified as Category D/X. FDA Category D. Hematologic toxicity and immunosuppression in the neonate. Increased risk of congenital malformations (cleft palate, skeletal anomalies) and fetal growth restrictio. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.