A Pilot Study to Evaluate the Safety and Efficacy of Mycophenolate Sodium (Myfortic®) in Combination With Sirolimus (Rapamune®) in Stable Renal Allograft Recipients

One-year graft survival after renal transplantation dramatically improved with the addition of calcineurin inhibitors (tacrolimus or cyclosporine) to maintenance immunosuppression regimens. Much of this improvement in early graft survival has been attributed to the efficacy of the calcineurin inhibitors in preventing early acute rejection episodes. However, long-term graft survival has not improved to as great of a magnitude as the improvements in short-term survival. In addition, research shows progressive decline in kidney function throughout the years post-transplantation. Clinical research now focuses on improving long term graft survival while maintaining long-term kidney function.

The leading cause of graft loss has been attributed to chronic allograft nephropathy (CAN). Risk factors for CAN include: prolonged ischemia time, delayed graft function, acute rejection episodes and calcineurin inhibitor nephrotoxicity (CIN). CIN has been identified as the most common identifiable contributor to CAN and the chief cause of late histologic injury and ongoing decline in renal function. At 10 years post-transplant, CIN has been found to be universally prevalent.

Calcineurin inhibitor minimization and elimination studies have sought to improve long-term allograft function by minimizing exposure to these nephrotoxic agents. Studies have demonstrated that early withdrawal of cyclosporine from a cyclosporine, sirolimus and steroid immunosuppression regimen at 3 months post-transplant improved renal function and graft survival at 48 months post-transplant. Other studies have demonstrated diminished prevalence of CAN at 2 years post-transplant in those patients maintained on sirolimus as compared with cyclosporine. Kidney function was also significantly improved with lower serum creatinine and higher GFR in the sirolimus maintenance group.

Sirolimus is a macrolide antibiotic immunosuppressive agent that exerts its mechanism of action by inhibiting the mTOR signaling cascade. In clinical trials, sirolimus was found to lack nephrotoxic effects when compared to cyclosporine. In kidney transplantation, multiple studies have demonstrated safety and efficacy of sirolimus in calcineurin inhibitor avoidance and withdrawal protocols.

Myfortic® (mycophenolate acid) is an enteric coated formulation of mycophenolic acid (MPA) approved for the prevention of rejection in kidney transplant recipients in combination with cyclosporine and corticosteroids. Myfortic® has no documented nephrotoxic effects. Mycophenolate mofetil (MMF), a prodrug of MPA also does not demonstrate nephrotoxic effects. Early studies have demonstrated therapeutic equivalence between Myfortic® and MMF both in de novo renal transplants and in conversion studies where MMF is converted to Myfortic at least 6 months after renal transplantation. Thus, studies demonstrating safety and efficacy of MMF with sirolimus in calcineurin inhibitor withdrawal protocols should also hold true using Myfortic® in such regimen.