Azathioprine

Indications
 Oral
Prophylaxis of rejection in organ and tissue transplant
Adult: 1-5 mg/kg/day. Adjust dose according to clinical response and haematological tolerance. Dose may also be given via IV admin.
Renal impairment: Dose adjustments may be needed.
Hepatic impairment: Dose adjustments may be needed.
Oral
Auto-immune diseases
Adult: 1-3 mg/kg/day. Discontinue treatment if there is no improvement after 12 wk.
Renal impairment: Dose adjustments may be needed.
Hepatic impairment: Dose adjustments may be needed.
Oral
Rheumatoid arthritis
Adult: Initially, 1 mg/kg/day given in 1-2 divided doses for 6-8 wk, may increase by 0.5 mg/kg every 4 wk until response or up to 2.5 mg/kg/day. Maintenance: Reduce dose gradually to achieve the lowest effective dose.
Renal impairment: Dose adjustments may be needed.
Hepatic impairment: Dose adjustments may be needed.
Intravenous
Renal homotransplantation
Adult: Usual initial doses: 3-5 mg/kg daily beginning at the time of transplantation. Usually given as a single dose on the day of transplantation, may be given 1-3 days before transplantation in some cases. May reduce dose to maintenance levels at 1-3 mg/kg daily. May convert to use of oral tablets subsequently at the same dose level. Treatment discontinuation may be needed in cases of severe haematologic or other toxicity.
Renal impairment: Dose adjustments may be needed.
Hepatic impairment: Dose adjustments may be needed.

Special Populations: Dose in renal impairment: Crcl 10-50 mL/min: 75% of normal daily dose; Crcl <10 mL/min: 50% of normal daily dose.

Reconstitution: 10 ml of sterile water for Inj to be added to the vial containing 100 mg of the drug, giving a resultant concentration of 10 mg/ml. This may be given by slow IV inj or further diluted in saline or dextrose to be used as IV infusion usually over 30-60 minutes. Infusion periods of 5 minutes to 8 hr have been used.
Contraindications
 Hypersensitivity; previous treatment with alkylating agents; pregnancy, lactation.
Warnings / Precautions
 Increased risk of serious infections and neoplasia in chronic immunosuppression; leucopenia, thrombocytopenia, renal or hepatic impairment. Increased risk of haematologic toxicity in patients with thiopurine methyltransferase deficiency. Monitor CBC (including platelet count) wkly during 1st mth, twice mthly for 2nd and 3rd mth, then mthly; monitor more frequently if there are dosage adjustments. Monitor LFT periodically; discontinue treatment if jaundice occurs. Reduce dose promptly or withdraw drug temporary if there is rapid decrease/persistently low WBC or signs of bone marrow depression. Dose reduction may be necessary in patients with reduced TPMT (thiopurine methyltransferase) activity.
Adverse Reactions
 Fever, chills; bone marrow depression characterised by leucopenia, thrombocytopenia or anaemia; anorexia, nausea, diarrhoea; arthralgias; secondary infections; hepatotoxicity, rash, alopoecia.
Potentially Fatal: Myelosuppression, mutagenicity and carcinogenicity; veno-occlussive liver disease.
Overdose Reactions
 Symptoms include nausea, vomiting, diarrhoea and mild abnormalities in the liver function.
Drug Interactions
 Increased risk of haematotoxicity with aminosalicylates, drugs that affect myelopoesis e.g. co-trimoxazole or trimethoprim. Increased risk of infections with intra-uterine devices and live vaccines. Increased risk of leucopenia with ACE inhibitors. Concurrent use may reduce the anticoagulant effect of vitamin K antagonists e.g. warfarin. Increased risk of myelosuppressive effects when used with drugs that inhibit TPMT (thiopurine methyltransferase) or xanthine oxidase e.g. olsalazine, allopurinol.
Potentially Fatal: Increased risk of serious haematotoxicity or hepatotoxicity with leflunomide. Increased risk of bone marrow suppression with mycophenolate mofetil. Increased risk of infections and malignancies with efalizumab.
See Below for More azathioprine Drug Interactions
Food Interactions
 Avoid cat's claw and echinacea.
Mechanism of Actions
 Azathioprine is an imidazolyl derivative of mercaptopurine, which inhibits DNA, RNA and protein synthesis and antagonises purine synthesis. It also inhibits mitosis and interferes with cellular metabolism of susceptible organisms. Azathioprine inj should be converted to oral therapy as soon as the drug can be tolerated.
Absorption: Well absorbed from the GI tract (oral).
Distribution: Protein-binding: About 30%. Crosses placenta.
Metabolism: Converted hepatically to 6-mercaptopurine which is further metabolised in the liver and GI tract via 3 main pathways: Hypoxanthine guanine phosphoribosyltransferase (to 6-thioguanine-nucleotides), xanthine oxidase (to 6-thiouric acid), and thiopurine methyltransferase (TPMT), which forms 6-methylmercapotpurine (6-MMP).
Excretion: Via the urine (mainly as metabolites). Half-life elimination: Parent drug (12 minutes); mercaptopurine (0.7-3 hr); prolonged in end stage renal disease.
Administration
 May be taken with or without food. (Preferably taken w/ or after meals to reduce GI discomfort.)
Storage Conditions
 Intravenous: Powder for inj: Store intact vials between 15-25°C. Protect from light. Reconstituted solution: Stable for up to 2 wk at room temperature or up to 4 days refrigerated, however, manufacturer recommends use within 24 hr of reconstitution. Oral: Store between 15-25°C.
ATC Classification
 L04AX01 - azathioprine ; Belongs to the class of other immunosuppressive agents.
Storage
 Intravenous: Powder for inj: Store intact vials between 15-25°C. Protect from light. Reconstituted solution: Stable for up to 2 wk at room temperature or up to 4 days refrigerated, however, manufacturer recommends use within 24 hr of reconstitution. Oral: Store between 15-25°C.
Available As
  • Azathioprine 25 mg
  • Azathioprine 50 mg

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