Neoral versus Sandimmun: clinical impact and modification of immunosuppressive therapy in cardiac transplantation

Immunosuppression for heart transplantation: where are we now?

The success of cardiac transplantation is largely attributable to the development of effective immunosuppressive regimens. The introduction of calcineurin inhibitors was pivotal in reducing the frequency of acute rejection and improving early survival. Newer agents, including mycophenolate mofetil (MMF) and proliferation-signal inhibitors, have shown promise in further reducing acute-rejection rates and, notably, reducing the frequency of cardiac allograft vasculopathy, which limits long-term graft survival. The introduction of first-year intravascular ultrasonography results as a surrogate marker for outcome after cardiac transplantation has helped assessment of the efficacy of immunosuppressive medications. Proliferation-signal inhibitors and MMF were shown by this imaging method to reduce cardiac allograft vasculopathy. The combination of these drugs, in tandem with the weaning of patients off calcineurin inhibitors, has been shown to reverse calcineurin-inhibitor-related nephrotoxic effects. A randomized trial that compared three of the more common immunosuppressive regimens suggested that tacrolimus and MMF are associated with a reduction in the frequency of rejection episodes that require treatment and have the fewest adverse effects. Finally, the use of statins has brought added benefit to immunosuppressive regimens by improving outcomes after cardiac transplantation, reportedly because of an immunomodulatory property. Promising newer immunosuppressive agents await clinical trials. This review presents an overview of the emerging data on immunosuppressive therapy for cardiac transplantation.

Immunosuppression, diagnosis, and treatment of cardiac allograft rejection

The success of cardiac transplantation has been largely attributable to the development of effective immunosuppressive regimens. The calcineurin inhibitors were pivotal in reducing the frequency of acute rejection and improving early survival. Newer agents, including mycophenolate mofetil and proliferation signal inhibitors, show some promise in further reducing episodes of acute allograft rejection and also having a significant impact on reducing transplant vasculopathy. The role of cytolytic induction therapy remains unclear, although its use may be most appropriate in the high risk presensitized transplant recipient. While the endomyocardial biopsy remains the gold standard for the diagnosis of acute allograft rejection, its invasive nature makes the test suboptimal. The presence of biopsy 'negative' rejection has also led to an appreciation for the role of antibody-mediated rejection in cardiac allograft dysfunction. Effective noninvasive evaluation of allograft rejection remains the ultimate challenge. While imaging technologies have some utility because of their ease of use, more sophisticated techniques such as gene-expession analysis from peripheral blood may show the greatest promise. Management of established acute allograft rejection has significantly improved with our understanding of the immune mechanisms involved. Therapies may be targeted specifically at cellular or humoral components of the immune system.

Cardiac transplant experience with cyclosporine

The advent of cyclosporine 20 years ago was a major advance in the field of solid organ transplantation. Its use enabled directed immunosuppression with a consequent decrease in the incidence of graft failure, acute rejection, and systemic infection. The early oil-based preparation, however, was difficult to administer and had limited bioavailability and unpredictable pharmacokinetics. The drug also has a fairly narrow therapeutic window with major long-term side effects, which include nephrotoxicity, malignancy, hyperlipidemia, and hypertension. The introduction of a microemulsion preparation (Neoral) with improved bioavailability has been associated with lower rates of rejection and comparable tolerability, therefore allowing the use of lower doses. Traditionally cyclosporine toxicity has been minimized by monitoring trough levels. Monitoring of levels 2 hours after dosing may provide a more accurate determination of cyclosporine exposure. The next phase in cardiac transplantation immunosuppression will most likely see a significantly diminished role for cyclosporine with the introduction of newer, more potent immunosuppressive agents with more favorable side-effect profiles. These agents, which include mycophenolate mofetil, sirolimus, and everolimus, also hold the promise of having a major impact on the development of transplant vasculopathy, which up to now has been an important determinant of limiting long-term allograft survival.

Neoral use in the cardiac transplant recipient

CyA is the core immunosuppressant of choice for the majority of transplant patients. The introduction of Neoral, a new microemulsion formulation of CyA. and more recently a range of adjunctive immunosuppressants have further enhanced the efficacy and tolerability of CyA-based immunosuppression. In the first year following transplantation the major causes of morbidity and death are graft failure, acute rejection, and systemic infection. Patients with deteriorated pulmonary circulation before transplantation are at increased risk of early postoperative death. Risk factors for early acute rejection include female donor sex, young donor age, and multiple HLA-DR mismatches. The principal cause of death in the long term is graft vasculopathy which accounted for 40% of all deaths. Risk factors that have been hypothesized to play a role in the pathogenesis of graft vasculopathy include hyperlipidemia, recipient age and gender, donor age, the number of HLA AB and DR mismatches, and CMV infection. Strategies proposed to reduce the risk of graft vasculopathy include aggressive use of lipid-lowering agents, avoidance of low CyA doses, and the use of adjunctive rapamycin or RAD therapy. Rejection surveillance therefore relies on routine serial endomyocardial biopsy. Recent research suggests that a more accurate assessment of the state of the graft can be obtained by considering the results across a number of biopsy samples obtained from different parts of the heart, rather than basing clinical judgment on the worst single result obtained. New molecular markers such as granzyme A mRNA are likely to improve the power of histology to diagnose and predict rejection. Neoral pharmacokinetics give greater bioavailability and less intrapatient variability than Sandimmune. In the keynote OLN 351 study comparing Neoral with Sandimmune in de novo heart transplant recipients, fewer Neoral patients needed antilymphocyte therapy to treat rejection, fewer female patients had rejection episodes in the Neoral group, the tolerability of the two formulations was equivalent, and there was a lower incidence of infections in the Neoral group. The clinical impact of Neoral in comparison with Sandimmune in de novo heart transplant patients has been investigated in a number of additional trials, including long-term studies, which have confirmed that Neoral is associated with: Lower CyA doses than Sandimmune. Equal or greater antirejection efficacy than Sandimmune. Comparable tolerability to Sandimmune. During the administration of intravenous CyA as an induction therapy in the days immediately following transplantation, there is evidence to suggest that a 6-hour infusion given twice daily, which mimics the pharmacokinetic profile of oral dosing, may be clinically more effective than a continuous 24-hour infusion. Milligram-for-milligram dose conversion from Sandimmune to Neoral is feasible. Following conversion, a reduction in the CyA dose may be required in the majority of patients to maintain target levels. In pediatric patients, the rate of elimination of CyA is greater and bioavailability increases with increasing age. Younger patients (less than 8 years of age) may be managed more effectively with a 3-times-daily, rather than a twice-daily dosing schedule. A number of studies have compared the clinical effects of Sandimmune and Neoral in maintenance therapy for cardiac transplant patients. As with de novo patients, these studies have found the new formulation of CyA to be associated with lower rates of acute rejection, lower therapeutic doses, and comparable tolerability. Milligram-to-milligram conversion from the old to the new CyA formulation is generally well tolerated, although in a minority of patients there is a significant increase in CyA levels. These may be associated with a transient increase in side effects which resolve on dose reduction. There is a dose-sparing effect with Neoral. Routine monitoring of both CyA and serum creatinine levels are adv