Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
AZATHIOPRINE vs ASTAGRAF XL
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 nucleotide synthesis, thereby suppressing DNA replication and cell proliferation. It is converted to 6-mercaptopurine, which acts as a purine antagonist, inhibiting de novo purine synthesis and interfering with RNA and DNA synthesis, particularly in rapidly dividing cells such as T-lymphocytes.
Calcineurin inhibitor that binds to FKBP-12, forming a complex that inhibits calcineurin, thereby preventing dephosphorylation and nuclear translocation of NFAT, which reduces T-cell activation and cytokine production (e.g., IL-2).
Renal transplant rejection prophylaxis (FDA),Rheumatoid arthritis (FDA),Off-label: autoimmune hepatitis, systemic lupus erythematosus, inflammatory bowel disease (Crohn's disease, ulcerative colitis), pemphigus, myasthenia gravis, dermatomyositis/polymyositis,Off-label: myelodysplastic syndrome, refractory immune thrombocytopenic purpura, atopic dermatitis, Behçet's syndrome
Prophylaxis of organ rejection in kidney transplant recipients,Prophylaxis of organ rejection in liver transplant recipients,Prophylaxis of organ rejection in heart transplant recipients
1.5 to 2.5 mg/kg orally once daily; typical adult dose 50-150 mg/day orally. Intravenous dose is 3-5 mg/kg/day as a slow infusion over 30-60 minutes.
Initial oral dose of 0.1-0.15 mg/kg/day divided every 12 hours, with subsequent adjustments based on trough levels. Typical maintenance dose 0.05-0.15 mg/kg/day.
Terminal elimination half-life of azathioprine is approximately 2–5 hours; its active metabolite 6-mercaptopurine has a half-life of 1–2 hours, but 6-thioguanine nucleotides accumulate in red blood cells with a half-life of several days, correlating with myelosuppression.
Terminal elimination half-life is approximately 43 hours (range 15.8–68.6 hours) in adult kidney transplant recipients. This long half-life supports once-daily dosing. In liver transplant patients, half-life ranges from 12 to 42 hours.
Azathioprine is metabolized by xanthine oxidase (XO) and thiopurine methyltransferase (TPMT) to active (6-mercaptopurine) and inactive metabolites. 6-Mercaptopurine is further metabolized by XO to 6-thiouric acid and by TPMT to 6-methylmercaptopurine. Genetic deficiency of TPMT increases risk of toxicity.
Primarily hepatic via CYP3A4 and CYP3A5; undergoes extensive first-pass metabolism. Substrate of P-glycoprotein.
Renal (approximately 2% as unchanged drug, 30% as 6-thiouric acid and other metabolites); biliary/fecal (minor, <10% as metabolites).
Primarily fecal (94.6%) via biliary elimination. Renal excretion accounts for approximately 2.4% of the dose, mainly as metabolites. Less than 1% is excreted unchanged in urine.
Approximately 30% bound, primarily to albumin.
Approximately 99% bound to plasma proteins, primarily albumin and alpha-1-acid glycoprotein.
0.8–1.0 L/kg, indicating distribution into total body water; extensive distribution into tissues including liver and erythrocytes.
Volume of distribution is 3.5–4.5 L/kg (wide distribution, indicating extensive tissue binding). High Vd reflects distribution into erythrocytes, lymphocytes, and tissues.
Oral bioavailability of azathioprine is 60–80% (mean 70%) with interindividual variability; absorption may be reduced by food.
Oral bioavailability is highly variable, approximately 20–30% (range 5–89%). Absorption is incomplete and inconsistent; food decreases absorption by up to 33%. The modified-release formulation (Astagraf XL) has a lower peak and more sustained absorption compared to immediate-release.
GFR >50 m L/min: no adjustment. GFR 10-50 m L/min: administer 75% of normal dose. GFR <10 m L/min: administer 50% of normal dose. Hemodialysis: administer 50% of normal dose after dialysis.
For GFR <30 m L/min: reduce dose by 50% and monitor trough levels closely. No adjustment for GFR >30 m L/min.
Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose by 25-50%. Child-Pugh Class C: contraindicated or use with extreme caution; reduce dose by at least 50%.
Child-Pugh Class A: no adjustment. Class B: reduce dose by 25%. Class C: reduce dose by 50% and monitor trough levels frequently.
1.5 to 2.5 mg/kg orally once daily; maximum 150 mg/day. For inflammatory bowel disease: 2-3 mg/kg/day. Intravenous: 3-5 mg/kg/day as a slow infusion.
Initial oral dose 0.15-0.2 mg/kg/day divided every 12 hours. Adjust to target trough levels of 5-15 ng/m L. Maximum dose 0.3 mg/kg/day.
Initiate at lower end of dosing range (1.5 mg/kg/day) due to potential for decreased renal and hepatic function; monitor renal function and hematologic parameters closely.
Start at lower end of adult dosing range (0.05 mg/kg/day) and titrate slowly due to reduced renal function and increased risk of adverse effects. Monitor trough levels closely.
Malignancy: Patients receiving immunosuppressive therapy including azathioprine have an increased risk of developing lymphoma and other malignancies, particularly skin cancers. The risk is related to the duration and intensity of immunosuppression. Hematologic toxicity: Severe leukopenia, thrombocytopenia, and anemia, which may be dose-related, can occur. Regular monitoring of blood counts is required. Hepatotoxicity: Hepatotoxicity, including fatal liver injury, has been reported, particularly at high doses.
Increased susceptibility to infection and possible development of lymphoma and other malignancies, particularly of the skin, due to immunosuppression. Increased nephrotoxicity, especially when used with other nephrotoxic drugs.
Hematologic monitoring: regular CBCs; Increased risk of infection; Hepatotoxicity; Pancreatitis; Carcinogenicity (lymphoma, skin cancer); TPMT deficiency increases myelotoxicity; Vaccination (live vaccines contraindicated); Renal and hepatic impairment; Drug interactions: allopurinol (reduce dose by 75%), ACE inhibitors (anemia), warfarin (anticoagulant effect decreased).
Nephrotoxicity, neurotoxicity (tremor, headache, seizures), hypertension, hyperkalemia, hyperglycemia, increased risk of infections and malignancies (especially skin), and lymphoproliferative disorders. Monitor blood pressure, renal function, electrolytes, and drug levels.
Hypersensitivity to azathioprine or 6-mercaptopurine; Pregnancy (unless benefit outweighs risk) - Category D; Lactation; Patients with TPMT deficiency (increased risk of severe myelotoxicity); Severely depressed bone marrow function; Active infections; Concurrent use of live vaccines; Pre-existing malignancy (except in organ transplantation context).
Hypersensitivity to tacrolimus or any component of the formulation; concurrent use with cyclosporine or other calcineurin inhibitors.
No known significant food interactions. Avoid grapefruit juice? (No interaction reported). Maintain consistent diet; no specific restrictions. Limit alcohol due to hepatotoxicity risk.
Grapefruit juice significantly increases tacrolimus AUC and Cmax; avoid concurrent use. High-fat meals may decrease absorption; maintain consistent fat intake with each dose to ensure stable levels. Avoid taking with alcohol or herbal supplements like St. John's wort, which may reduce efficacy.
Azathioprine is pregnancy category D. First trimester: increased risk of congenital anomalies including ventricular septal defects, limb defects, and esophageal atresia. Second and third trimesters: risk of intrauterine growth restriction, preterm birth, and neonatal immunosuppression (leukopenia, thrombocytopenia). Use only if benefit outweighs risk.
Tacrolimus is classified as FDA Pregnancy Category C. There are no adequate and well-controlled studies in pregnant women. In animal studies, tacrolimus caused maternal toxicity and embryotoxicity at doses higher than those used clinically. First trimester exposure is associated with an increased risk of congenital anomalies, including cardiac malformations. Second and third trimester use has been linked with intrauterine growth restriction, preterm delivery, and transient neonatal hyperkalemia and renal dysfunction. Postnatal immunosuppression in the neonate may occur.
Azathioprine is excreted into breast milk in low concentrations. M/P ratio is approximately 0.7. Nursing infants of mothers on azathioprine have not shown adverse effects; however, theoretical risk of immunosuppression exists. Caution is advised; monitor infant for increased infections.
Tacrolimus is excreted into human breast milk with a milk-to-plasma (M/P) ratio of approximately 0.3. Limited data suggest low infant exposure (relative infant dose 0.5% of maternal weight-adjusted dose). However, because of potential for infant immunosuppression and growth effects, breastfeeding is generally not recommended unless benefits outweigh risks. Monitor infant for trough levels if breastfeeding.
Pharmacokinetic changes in pregnancy include increased clearance and decreased absorption. Dose may need adjustment to maintain therapeutic efficacy. Close monitoring of disease activity and drug levels (6-thioguanine nucleotide levels) is recommended. No standard dose adjustment; individualization required.
Pregnancy increases tacrolimus clearance due to expanded plasma volume and altered cytochrome P450 3A4 activity. Dose requirements may increase by 25-50% during the second and third trimesters. Therapeutic drug monitoring is essential, targeting trough levels 5-10 ng/m L. Postpartum, doses should be reduced to prepregnancy levels within 1-2 weeks as clearance normalizes.
Monitor CBC and LFTs weekly for first month, then biweekly for 2 months, then monthly. TPMT genotype testing before initiation. Avoid concurrent allopurinol unless dose reduced to 25% of original. Use with caution in renal impairment. May cause hepatotoxicity, pancreatitis, or lymphoproliferative disorders.
Monitor trough levels 5-15 ng/m L; avoid using with sirolimus due to increased risk of thrombotic microangiopathy; conversion from tacrolimus immediate-release is 1:1 (mg:mg) but monitor levels closely for 2 weeks; administer consistently with or without food to avoid fluctuations.
Take exactly as prescribed; do not double dose if missed.,Avoid live vaccines during treatment and for 3 months after stopping.,Report any signs of infection, unexplained bruising/bleeding, or jaundice immediately.,Limit sun exposure and use sunscreen due to increased skin cancer risk.,Do not take allopurinol or other new medications without consulting doctor.,Maintain adequate hydration to reduce risk of hepatotoxicity.,Regular blood tests are required to monitor for side effects.
Take at the same time every day, consistently with or without food.,Do not crush, chew, or split the extended-release capsules; swallow whole.,Avoid grapefruit and grapefruit juice as they can increase drug levels and toxicity.,Report signs of infection (fever, sore throat), tremors, or changes in urine output immediately.,Minimize sun exposure and use sunscreen due to increased risk of skin cancer.,Do not change brand or formulation without consulting your transplant team.,Keep all appointments for blood level monitoring.
"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."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about AZATHIOPRINE vs ASTAGRAF XL, answered by our medical review team.
AZATHIOPRINE is a Immunosuppressant that works by Azathioprine is a purine analog that inhibits purine nucleotide synthesis, thereby suppressing DNA replication and cell proliferation. It is converted to 6-mercaptopurine, which acts as a purine antagonist, inhibiting de novo purine synthesis and interfering with RNA and DNA synthesis, particularly in rapidly dividing cells such as T-lymphocytes.. ASTAGRAF XL is a Immunosuppressant, Calcineurin Inhibitor that works by Calcineurin inhibitor that binds to FKBP-12, forming a complex that inhibits calcineurin, thereby preventing dephosphorylation and nuclear translocation of NFAT, which reduces T-cell activation and cytokine production (e.g., IL-2).. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between AZATHIOPRINE and ASTAGRAF XL 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 AZATHIOPRINE is: 1.5 to 2.5 mg/kg orally once daily; typical adult dose 50-150 mg/day orally. Intravenous dose is 3-5 mg/kg/day as a slow infusion over 30-60 minutes.. The standard adult dose of ASTAGRAF XL is: Initial oral dose of 0.1-0.15 mg/kg/day divided every 12 hours, with subsequent adjustments based on trough levels. Typical maintenance dose 0.05-0.15 mg/kg/day.. 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 AZATHIOPRINE and ASTAGRAF XL 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. AZATHIOPRINE is classified as Category D/X. Azathioprine is pregnancy category D. First trimester: increased risk of congenital anomalies including ventricular septal defects, limb defects, and esophageal atresia. Second and. ASTAGRAF XL is classified as Category C. Tacrolimus is classified as FDA Pregnancy Category C. There are no adequate and well-controlled studies in pregnant women. In animal studies, tacrolimus caused maternal toxicity an. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.