Azathioprine

Administration

• Type: immunosuppressant
• Dosage Forms: tablet, powder for injection (IV form unavailable in US)
• Dosage Strengths: tablet: 50, 75, 100mg; powder for injection: 100mg/vial
• Routes of Administration: PO, IV (unavailable in US)
• Common Trade Names: Azasan, Imuran

Adult Dosing

Kidney transplant rejection prophylaxis

• 1-3mg/kg PO QD
• Start: 3-5mg/kg PO x1 up to 3 days before transplant; Info: transplant protocols may vary

Rheumatoid arthritis, severe

• 1-2.5mg/kg/day PO divided QD-bid
• Start: 1mg/kg/day PO divided QD-bid; Max: 2.5mg/kg/day; Info: after 6-8wk may increase 0.5mg/kg/day q4wk

Crohns Disease

• 100-250mg PO QD
• Start: 50mg PO QD; Max: 2.5mg/kg/day; Info: for induction or remission maintenance and fistulizing disease, steroid-sparing effects

Ulcerative colitis

• 100-250mg PO QD
• Start: 50mg PO QD; Max: 2.5mg/kg/day; Info: for induction or remission maintenance, steroid-sparing effects

Pediatric Dosing

Kidney transplant rejection prophylaxis

• 1-3mg/kg PO QD
• Start: 3-5mg/kg PO x1 up to 3 days before transplant; Info: transplant protocols may vary

Juvenile idiopathic arthritis, severe

• 1-2.5mg/kg/day PO divided QD-bid
• Start: 1mg/kg/day PO divided QD-bid; Max: 2.5mg/kg/day; Info: after 6-8wk may increase 0.5mg/kg/day q4wk

Special Populations

• Pregnancy Rating: Pregnancy Category D
• Lactation risk: possibly unsafe

Renal Dosing

• Adult: CrCl 10-50: decrease dose 25%; CrCl <10: decrease dose 50%; HD: give 0.25mg/kg supplement; PD: not defined
• Pediatric: CrCl 10-50: decrease dose 25% or give q36h; CrCl <10: decrease dose 50% or give q48h; HD: give supplement; PD: not defined

Hepatic Dosing

• Adult: not defined; caution advised
• Pediatric: not defined; caution advised

Contraindications

• Allergy to class/drug
• pregnancy (RA use)
• caution if renal impairment
• caution if prior alkylating agents

Adverse Reactions

Serious

• leukopenia
• thrombocytopenia
• anemia
• myelosuppression
• immunosuppression
• infection
• PML
• GI hypersensitivity reaction
• pancreatitis
• hepatotoxicity
• hepatic veno-occlusive disease
• lymphoma
• malignancy
• acute febrile neutrophilic dermatosis

Common

• leukopenia
• thrombocytopenia
• anemia
• infection
• nausea
• vomiting
• anorexia
• diarrhea
• ALT, AST elevated
• malaise
• myalgia
• fever
• rash
• malignancy

Pharmacology

• Half-life: 5 hours
• Metabolism: liver extensively, erythrocytes; CYP450
• Excretion: bile, urine (1-2% unchanged)

Mechanism of Action

Acts as a prodrug for mercaptopurine, inhibiting an enzyme required for the synthesis of DNA. Thus, it most strongly affects proliferating cells, such as the T cells and B cells of the immune system

See Also

• Transplant complications

References

• A randomised clinical trial comparing prednisone and azathioprine in myasthenia gravis. Results of the second interim analysis. Myasthenia Gravis Clinical Study Group. J Neurol Neurosurg Psychiatry. 1993;56(11):1157-1163. [PubMed 8229026]
• American College of Rheumatology Ad Hoc Committee on Clinical Guidelines, “Guidelines for Monitoring Drug Therapy in Rheumatoid Arthritis,” Arthritis Rheum, 1996, 39(5):723-31. [PubMed 8639168]
• Astey AV, Wakelin S, and Reynolds NJ, “Guidelines for Prescribing Azathioprine in Dermatology,” Br J Dermatol, 2004, 151(6):1123-32. [PubMed 15606506]
• Armuzzi A, Felice C, Papa A, et al. Prevention of postoperative recurrence with azathioprine or infliximab in patients with Crohn's disease: an open-label pilot study. J Crohns Colitis. 2013;7(12):e623-e629. doi: 10.1016/j.crohns.2013.04.020. [PubMed 23810678]
• Arnold DM, Nazi I, Santos A, et al, “Combination Immunosuppressant Therapy for Patients With Chronic Refractory Immune Thrombocytopenic Purpura,” Blood, 2010, 115(1):29-31. [PubMed 19897578]
• Aronoff GR, Bennett WM, Berns JS, et al, Drug Prescribing in Renal Failure: Dosing Guidelines for Adults and Children, 5th ed. Philadelphia, PA: American College of Physicians; 2007, p 97, 177.
• Azasan (azathioprine) [prescribing information]. Bridgewater, NJ: Salix Pharmaceuticals; March 2019.
• Azathioprine injection [prescribing information]. Eatontown, NJ: West-Ward Pharmaceuticals; August 2015.
• Baum D, Bernstein D, Starnes VA, et al, “Pediatric Heart Transplantation at Stanford: Results of a 15-Year Experience,” Pediatrics, 1991, 88(2):203-14. [PubMed 1861916]
• Beissert S, Werfel T, Frieling U, et al, "A Comparison of Oral Methylprednisolone Plus Azathioprine or Mycophenolate Mofetil for the Treatment of Pemphigus," Arch Dermatol, 2006, 142(11):1447-54. [PubMed 17116835]

epocrates