Azathioprine

CLINICAL USE

Immunosuppressive:

  • Prophylaxis of transplant rejection
  • Treatment of various auto-immune conditions

    DOSE IN NORMAL RENAL FUNCTION

    1–5 mg/kg/day

    PHARMACOKINETICS

  • Molecular weight                           :277.3
  • %Protein binding                           :<30
  • %Excreted unchanged in urine     : <2
  • Volume of distribution (L/kg)       :0.55–0.8
  • half-life – normal/ESRD (hrs)      :3–5/Increased

    DOSE IN RENAL IMPAIRMENT

    GFR (mL/MIN)

  • 20 to 50     : Dose as in normal renal function
  • 10 to 20     : 75–100%
  • <10           : 50–100%

    DOSE IN PATIENTS UNDERGOING RENAL REPLACEMENT THERAPIES

  • CAPD                :Dialysed. Dose as in normal renal function
  • HD                     :Dialysed. Dose as in normal renal function
  • HDF/high flux   :Dialysed. Dose as in normal renal function
  • CAV/VVHD      :Dialysed. Dose as in normal renal function

    IMPORTANT DRUG INTERACTIONS

    Potentially hazardous interactions with other drugs

  • Allopurinol: enhances effect with increased toxicity. Reduce azathioprine dose by 50–75% if administered concomitantly
  • Antibacterials: increased risk of haematological toxicity with co-trimoxazole
  • Anticoagulants: possibly reduced anticoagulant effect of coumarins
  • Antipsychotics: avoid concomitant use with clozapineCiclosporin: ?decreased ciclosporin absorption and bioavailability
  • Cytotoxic agents may be additive or synergistic in producing toxicity, particularly on the bone marrow

    ADMINISTRATION

    Reconstition

    Add 5 mL water for injection to each vial (50 mg)

    Route

    Oral, IV

    Rate of Administration

    Over not less than 1 minute

    Comments

  • Some units dilute to 100 mL sodium chloride or glucose 5% and infuse over 1 hour.
  • IV bolus peripherally, preferably in the side arm of a fast-running infusionVery irritant to veins. Flush with 50 mL sodium chloride 0.9% after administration
  • Take tablets with or after food

    OTHER INFORMATION

    Extensively metabolised to mercaptopurine

  • 1 mg by IV injection is equivalent to 1 mg by oral route
  • 6-mercaptopurine levels can be monitored in patients with low urate clearance
  • Monitor white cell and platelet counts
  • Cytotoxic Drug – Do Not Handle Can be given as an intermittent infusion (up to 250 mg in 100 mL)
  • About 40–60% is removed by haemodialysis.
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