Malononitrilamides and tacrolimus additively prevent acute rejection in rat cardiac allografts

The novel immunosuppressive agents malononitrilamides (MNA) 279 and 715 are derivatives of A77 1726, the primary metabolite of leflunomide. The effect s of these agents have been previously demonstrated in rat skin and cardiac allo- and xenotransplant models. The aim of this study was to evaluate the combination of MNA and tacrolimus in a high-responder rat cardiac allotran splant model. Graft survival was evaluated following 10 days of post-transplant oral ther apy of MNA or tacrolimus alone and the drugs combined in PVG recipients of DA grafts. An iso-effect curve of single and combined drugs was constructed . Histological changes in grafts were evaluated at 10 days. MNA (20 mg/kg) or tacrolimus (2.4 mg/kg) alone prolonged graft survival wit h median survival of 14 and 13.5 days, respectively. Combined therapy of MN A (10 mg/kg) and tacrolimus 1.6 mg/kg likewise resulted in a median surviva l of 13.25 days and an iso-effect curve for these doses was constructed. An other iso-effect curve for median graft survival of 18-19 days, including M NA (10 mg/kg) + tacrolimus (3.2 mg/kg) in combination, MNA (30 mg/kg) alone and tacrolimus (4.8 mg/kg) alone, was constructed and both isoboles showed a straight line, demonstrating additive effects (zero interaction). In add ition, histological analysis of grafts confirmed the benefit of the drug co mbination. No additional toxicity was noted with combined therapy. Optimal doses of MNA or tacrolimus had comparative effects on graft surviva l and histological changes, and a combination of the two drugs was benefici al with respect to both these parameters. The iso-effect curves Verified ad ditive effects of the drug combination.