This clinical trial is focused on patients who have undergone a kidney transplant due to kidney failure. The study is examining the use of a medication called tacrolimus, which is commonly used to help prevent the body from rejecting a transplanted kidney. The trial involves two different forms of tacrolimus: Advagraf and Envarsus, both of which are prolonged-release medications. These medications are designed to release the active ingredient slowly over time, which can help maintain stable levels in the body.

The purpose of the study is to determine if the dose of Envarsus can be reduced compared to Advagraf while still maintaining effective levels of tacrolimus in the body. Participants in the study will take one of these medications orally, and their tacrolimus levels will be monitored to ensure they remain within a therapeutic range. The study will also look at whether switching to Envarsus results in fewer pills to take, fewer side effects, and more consistent medication levels in the body.

Throughout the study, researchers will also explore if certain genetic factors, like the presence of the CYP3A5*1 allele, should be considered when prescribing these medications. The trial aims to provide insights into the best dosing strategies for patients who require higher doses of tacrolimus to prevent organ rejection. The study is expected to continue until early 2026.