Azathioprine is also an immunosuppressive agent used in the transplantation program. It has been used in a number of inflammatory forms of arthritis for the past 4 decades with success. It has not been shown to work for the psoriasis, but does work for the joint manifestations and might be used in individuals who have primarily joint disease with minimal skin involvement.
Mode of administration
Azathioprine is given by mouth at a dose of 1.5-2.5 mg /Kg /day. It comes in tables of 50 mg each, thus most people will require between 100 and 250 mg a day (2-5 tablets). It takes 3-4 months to appreciate a response with azathioprine.
Azathioprine may also suppress the bone marrow and is associated with an increased risk of infection. On rare occasions it may cause an allergic skin rash or liver reaction. There are individuals who lack the enzyme that breaks down azathioprine and these people would be very susceptible to toxic reactions with even low doses of azathioprine. When starting azathioprine patients should have a blood test done at one week to assure that they have not reduced their white blood cell count. Once a stable dose has been achieved, hematological blood tests should be repeated at monthly intervals. If the white blood cell count is low, the drug must be stopped, although it may be re-administered in a lower dose.