Azathioprine is an immunosuppressive drug that is widely used in a variety of immune-mediated disorders. A meta-analysis of five double-blind and two single-blind, randomised, controlled trials involving a total of 793 MS patients supported the conclusion that oral azathioprine (1–3 mg/kg/m2) reduces the rate of relapse and might have a very small effect on EDSS scores. These results have been criticised on the basis that inadequate azathioprine doses were used in some of these trials. Another recent meta-analysis of published studies suggested that azathioprine may have a similar effect on two-year probability of freedom from relapse to the interferons in reducing relapse rate. A number of trials are currently in progress to determine the potential treatment effects of azathioprine administered either alone or in combination with the interferons. Side-effects include gastrointestinal, haematological, and hepatic toxicity. Another potential risk of long-term therapy is cancer, although a case-controlled study suggests that short-term use (less than five years) is not associated with a significantly increased risk. Careful monitoring of the patient (including blood cell counts and liver function tests) is necessary throughout the course of treatment.

In the opinion of the Committee, therapy with azathioprine has been demonstrated to have limited usefulness in selected patients. Although it is generally well tolerated, its use carries risk.