Thiopurine methyltransferase deficiency has been associated with intolerance to azathioprine.Our goals were to assess the frequency of enzyme deficiency in autoimmune hepatitis and correlate deficiency states with azathioprine intolerance.Eighty-six patients receiving azathioprine(50-150 mg daily) were evaluated for enzyme activity and azathioprine-related complications.Their findings were compared to 89 similarly treated but untested patients.Thirteen patients(15%) had low thiopurine methyltransferase levels(11.4± 0.9 U/ml RBC;range,3.5-14.9 U/ml RBC) .Azathioprine intolerance occurred as commonly in patients with normal or above normal enzyme levels as in patients with below normal levels(12% versus 15%,p = 0.7) .Patients treated without enzyme testing had the same frequency of complications(9% versus 13%,p = 0.5) as tested patients.We conclude that routine screening of blood thiopurine methyltransferase levels has a low yield for identifying individual patients at risk for azathioprine toxicity during conventional low dose therapy for autoimmune hepatitis.
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