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

References

epocrates