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.

See how to identify renal failure stages according to GFR calculation

See how to diagnose irreversible renal disease

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