Azathioprine Therapy Guidelines

Initial Dosing and Monitoring

The British Journal of Dermatology recommends starting azathioprine at 50 mg daily (approximately 1 mg/kg/day for most adults) to minimize early gastrointestinal side effects 1
Take medication with or shortly after food to reduce nausea, as suggested by the British Journal of Dermatology 1
Consider splitting the daily dose if gastrointestinal symptoms occur, according to the British Journal of Dermatology 1
Maintain this initial dose for at least 4 weeks before considering dose increases, as recommended by the British Journal of Dermatology and Praxis Medical Insights 1, 2

Check thiopurine methyltransferase (TPMT) activity prior to initiating therapy, as recommended by the British Journal of Dermatology and Hepatology 1, 3
For normal TPMT activity, proceed with standard dosing protocol, according to the British Journal of Dermatology 1
For intermediate (heterozygous) TPMT activity, reduce dose (1-1.5 mg/kg/day), as suggested by Hepatology 3
For absent (homozygous deficient) TPMT activity, azathioprine is contraindicated, according to the British Journal of Dermatology 4, 1
Obtain baseline laboratory tests including complete blood count and liver function tests, as recommended by the British Journal of Dermatology 1, 5

Monitor full blood count (FBC) and liver function tests (LFTs) weekly for the first 4 weeks of therapy, as recommended by the British Journal of Dermatology 4, 5
Continue weekly monitoring until maintenance dose is achieved, according to the British Journal of Dermatology 5
After stable maintenance dose is established, reduce monitoring frequency to a minimum of once every 3 months, as suggested by the British Journal of Dermatology 4, 5
Avoid concomitant use with allopurinol, which inhibits xanthine oxidase and prolongs azathioprine action, potentially increasing toxicity, according to the British Journal of Dermatology 6
Live vaccines are contraindicated during azathioprine therapy, as recommended by the British Journal of Dermatology 6
Patients who have not had chickenpox should seek immediate attention if exposed to varicella zoster virus, according to the British Journal of Dermatology 7

The American Association for the Study of Liver Diseases recommends increasing the azathioprine dose to 2 mg/kg daily as the dose of prednisone is gradually withdrawn, and then continuing indefinitely as maintenance therapy 8, 9

The target maintenance dose of 2 mg/kg/day has shown 87% remission rates over a median follow-up of 67 months, with follow-up liver biopsy assessments showing inactive or minimal histological disease in 94% of patients 8
Long-term, probably permanent, maintenance treatment is advisable in patients after a relapse, according to the European Association for the Study of the Liver 10
As azathioprine dose increases, gradually taper prednisone dose by 2.5 mg each month, with the goal of completely withdrawing prednisone while maintaining disease control on azathioprine monotherapy 11, 10

Common side effects include withdrawal arthralgia (63%), lymphopenia (57%), and myelosuppression (7%) 8