Increased incidence of allograft rejection in stable heart transplant recipients after late conversion from mycophenolate mofetil to azathioprine.

Mycophenolate mofetil (MMF) is a safe and effective immunosuppressive agent in kidney and liver transplantation. Preliminary studies also support its use in heart transplantation. However, the cost of MMF is substantially greater than azathioprine (AZA), the current alternative. Since the majority of rejection episodes occur within the first few months of transplantation, using MMF early after transplantation and subsequently converting to AZA, after the risk of rejection has diminished, might be cost-effective. In order to evaluate the safety of such a strategy in heart transplant recipients, we reviewed the rejection profiles of a group of patients who were converted from MMF to AZA late after transplantation. Forty-three stable patients on chronic MMF therapy as part of an open-label, long-term safety study were converted to either commercially available MMF (CellCept) or AZA, at the conclusion of the study. Demographic variables, rejection histories before and after conversion, and immunosuppressive regimens were examined. Twenty-three patients were continued on commercial MMF and 20 were converted to AZA therapy. The average duration of MMF therapy prior to conversion was 41 months in each group. Baseline demographics were similar in the two groups. Treated allograft rejection occurred in 10 of 20 patients converting to AZA, as compared to only 1 of 23 patients remaining on MMF; p = 0.002. Additionally, mean scores (1-5 scale) for the three biopsies before and after conversion favored continued MMF therapy (1.5+/-0.6 before and 1.2+/-0.4 after conversion in MMF group vs. 1.3+/-0.5 before and 1.7+/-0.9 after conversion to AZA; p = 0.02). No allograft loss occurred as a result of conversion. These data suggest that conversion from MMF to AZA, even late after transplantation, can be associated with allograft rejection. The costs associated with these rejection episodes (the additional immunosuppressive agents, endomyocardial biopsies, and physician visits) may exceed the potential cost savings of converting stable heart transplant recipients from MMF to AZA.