Critical threshold of azathioprine dosage for maintenance immunosuppression in kidney graft recipients

Background. There are conflicting reports in the literature concerning the efficacy of maintenance immunosuppression in renal transplantation with a r egimen of azathioprine and steroids. Methods. The daily dosage (mg/kg) of azathioprine administered 1 year after transplantation was analyzed in relation to subsequent long-term graft out come. Transplants performed from 1985 to 1996 and reported to the Collabora tive Transplant Study were analyzed. Results. In patients on maintenance immunosuppression without cyclosporine, the daily dosage of azathioprine had a highly significant influence on lon gterm graft outcome. Patients who received >1.5 mg/kg/ day of azathioprine had a 69% graft survival rate at 7 years, compared with a 55% rate in patie nts receiving 1.01-1.5 mg/kg/day (P<0.0001) and a 45% rate in patients rece iving less than or equal to 1.00 mg/kg/day (P<0.0001). This observation was valid for patients who were taken off cyclosporine during the first year a s well as for patients who were treated with azathioprine and steroids (wit hout cyclosporine) from the beginning. Conclusion. Maintenance immunosuppression with azathioprine and steroids re sults in good long-term kidney graft survival, provided azathioprine is adm inistered at a daily dose of >1.5 mg/kg.