Pharmacokinetics-based Mycophenolate Mofetil Dosing for GVHD Prevention

Graft-versus-host disease (GVHD) remains a major barrier to the success of allogeneic blood and marrow transplant (BMT) therapy. Acute GVHD is seen in 30-80% of patients and once established, often responds poorly to therapy and is associated with chronic disease and increased risk of death. Although combination of methotrexate (MTX) and a calcineurin inhibitor has been the "standard of care" for more than a quarter of a century, there is little consensus on the most effective and least toxic approach to GVHD prevention. MTX use is associated with painful mucositis, delay in engraftment and potential pulmonary toxicity. For cord blood transplants, commonly, a calcineurin inhibitor is used with corticosteroids and antithymocyte globulin. Steroid therapy is frequently complicated by high rates of infection, hyperglycemia and hypertension. Mycophenolate mofetil (MMF), whose metabolite mycophenolic acid (MPA) inhibits proliferation of lymphocytes, is approved for prevention of organ transplant rejection. MMF in combination with CsA is widely used for GVHD prevention in patients receiving reduced-intensity conditioning BMT. It has also been successfully used in primary and salvage therapy of acute GVHD. In myeloablative transplants, while the GVHD outcomes appear comparable, this regimen appears to have superior toxicity profile in comparison to CsA and MTX with faster hematopoietic engraftment and reduced severity and duration of mucositis. One challenge with MMF use in BMT recipients is a significantly lower MPA exposure in the immediate post-conditioning period when compared to organ transplant recipients. This has been shown in a number of pharmacokinetics studies including our preliminary data on pediatric myeloablative transplants. Low total and unbound MPA trough concentrations are associated with higher rates of acute GVHD and graft rejection, and lower response rates in treatment of acute GVHD. There is also poor correlation between MPA trough concentration and area under the concentration curve (AUC). While most previous studies have used fixed MMF dosing, one recent study in adults has shown feasibility of AUC-based individualized MMF dosing. This protocol is based on the premise that optimization of MPA exposure in the immediate post-transplant phase will lead to better acute GVHD prevention. It will study an AUC-based targeting of MMF in pediatric patients undergoing myeloablative allogeneic BMT. We propose a novel continuous infusion method for MMF administration to achieve total MPA steady state concentration. Salient findings emerging from this study will be examined and in replicate cohorts of pediatric and adult patients undergoing allo-BMT.