Renal Tubular Injury and Transplant Outcomes in Cardiac Recipients Converting From IR Tacrolimus to XR Tacrolimus

Overview

Immediate release (IR) tacrolimus peaks in the first two hours after administration. These peak levels are influenced by CYP3A5 expression with expressors requiring higher total daily doses with higher peak levels compared to non-expressors. Tacrolimus XR (Envarsus) is a once daily formulation with delayed absorption and lower peak levels while maintaining similar trough levels as seen with IR tacrolimus. A randomized trial of conversion from IR tacrolimus to tacrolimus XR in kidney transplant recipients have shown similar efficacy and adverse events between the two groups but no improvement in estimated GFR. However, urinary biomarkers of acute kidney injury associated with changes in tacrolimus dosing may be more sensitive then serum creatinine. The objective of this study is to assess renal tubular injury in heart transplant recipients who are converted from immediate release to tacrolimus XR. The hypothesis is that the delayed absorption and lower peak levels of tacrolimus XR will lead to less tubular injury and improved renal function without increased risk to the heart allograft.

The primary outcome is change in urinary NGAL expression with conversion from IR tacrolimus to tacrolimus XR. In aim 1, changes in urinary biomarkers of tubular injury at 4 weeks after conversion to tacrolimus XR with stable trough levels will be assessed. These changes will be assessed by CYP3A5 expressor category that will be determined by genotyping of a single gene for variants. The changes in GFR using the creatinine-cystatin C CKD-EPI equation will be assessed. In aim 2, the rate of rejection as defined as treated rejection within the last 30 days for any grade \> 1R or AMR or acute graft dysfunction (LV ejection fraction drop \> 10%) will be looked. The cardiac allograft vasculopathy based on coronary angiography +/- IVUS and right heart catheterization hemodynamics at baseline and 1 year post conversion will also be evaluated. In addition to changes in cardiac function, the changes in blood pressure, serum glucose, and cholesterol in the first year after conversion will be assessed.