The goal of this clinical trial is to compare the bioavailability and practicability of two different formulations of tacrolimus in kidney transplant recipients. The main objective is to demonstrate that Envarsus® (test drug) has superior (higher) oral bioavailability compared with Advagraf™ (comparator drug) at 12 weeks after kidney transplantation. The trial also aims to compare the practicability (handling) of the two drugs using a series of pharmacokinetic parameters and to explore the relationship between drug bioavailability and long-term clinical outcomes, with a special focus on dose-dependent adverse reactions, measured until 3 years post-transplantation. The trial incorporates a pharmacokinetic sub-study designed to profile the peak tacrolimus blood concentration up to 6 hours after drug intake on the day of the 12-week study visit.

This clinical trial aims to compare the bioavailability and practicability of two alternative once-daily formulations of tacrolimus in patients who have received either a first or second kidney transplant and require prophylactic immunosuppressive treatment to prevent allograft rejection. Trial participants are randomised within 7 days prior to kidney transplantation surgery in a 1:1 ratio to two alternative treatment arms containing either Envarsus (test arm) or Advagraf (comparator arm) as first-line calcineurin inhibitor within a standard-of-care immunosuppressive regimen. Tacrolimus blood trough levels and drug doses are monitored at regular intervals to measure a dose-normalised trough level (concentration/dose, C/D ratio) as an estimate of tacrolimus bioavailability.

The primary objective is to demonstrate that the C/D ratio of tacrolimus measured in kidney transplant recipients treated with Envarsus® (test drug) is superior to (higher than) the C/D ratio measured in patients treated with Advagraf™ (comparator drug) at 12 weeks post-transplantation. The trial also aims to compare the practicability (handling) of these two once-daily drug formulations using a series of pharmacokinetic parameters that will measure the speed with which therapeutic blood trough levels are attained and the ease with which stable blood trough levels are maintained over time.

Secondarily, TaC:Drop aims to explore the relationship between the early C/D ratio measured at 12 weeks post-transplantation and later clinical outcomes measured until three years post-transplantation. The study aims to investigate whether a superior pharmacokinetic drug profile is associated with fewer and milder dose-dependent drug toxicities and superior kidney graft function, as measured by long-term safety and efficacy parameters.

Drug pharmacokinetics will be explored in greater detail during a sub-study designed to profile the peak blood concentration of Envarsus® and Advagraf™ at 12 weeks post-transplantation in patients who volunteer to provide three additional blood samples at two-hour intervals after drug intake on the day of the 12-week trial visit. Participation in this sub-study is voluntary and available to all trial centres and all trial patients.

Inclusion Criteria:

1. Signed and dated written informed consent
2. Adult (≥18 years old) male or female
3. Renal insufficiency necessitating kidney transplantation and approved to receive a first or second kidney allograft from a living or deceased organ donor
4. ABO blood type compatible with the donor kidney
5. Able to swallow an oral formulation of tacrolimus in tablet or capsule form

Exclusion Criteria:

1. Multi-organ transplantation
2. Any previous solid organ transplantation (other than a first kidney allograft)
3. For recipients of a second kidney transplant: loss of first kidney transplant within 2 years after transplantation owing to immunological reasons or recurrence of the underlying renal disease
4. Patient and/or donor is positive for HCV, HBV or HIV
5. History of any malignancy that could not be curatively treated
6. Ongoing abuse of drugs or alcohol
7. Signs of advanced liver disease or any signs of liver decompensation
8. Ongoing uncontrolled systemic infection
9. Severe diarrhoea, vomiting, active peptic ulcer, previous bariatric surgery, or any other gastrointestinal disorder that may affect absorption of tacrolimus
10. Planned or foreseeable use of cyclosporine, belatacept or any tacrolimus preparation other than Envarsus® or Advagraf™
11. Known contraindication or hypersensitivity to tacrolimus, and/or to any of the excipients listed in section 6.1 of the Summary of Product Characteristics (SmPC) of both Envarsus® and Advagraf™, and/or to any other macrolides
12. Pregnant or nursing (lactating) women, where pregnancy is defined as the state of a female after conception and until the termination of gestation, confirmed by a positive hCG laboratory test
13. Women of child-bearing potential (WOCBP), defined as all women physiologically capable of becoming pregnant, unless using a highly-effective method of contraception
14. Participation in another interventional clinical trial in the time period starting from 4 weeks prior to randomisation and throughout the entire trial period
15. Any condition or factor which, in the judgement of the investigator, would place the subject at undue risk, invalidate communication with the investigator or study team, or hamper compliance with the trial protocol or follow-up schedule
16. Inability to freely give informed consent (e.g. individuals under legal guardianship)