Conversion From Brand to Generic Tacrolimus in High Risk Transplant Recipients

Primary hypothesis:

- Generic immunosuppressants for which bioequivalence were established in single-dose healthy volunteer studies are also bioequivalent to the brand in stable transplant patients that are considered high-risk such as CYP3A expressors, AA, and diabetics patients under steady-state conditions and there will be no difference in intra-subject variability.

Secondary hypotheses:

• Generic immunosuppressants will be bioequivalent among each other in transplant patients independent of the type of risk (CYP3A5 expression, race, diabetes, age or a combination hereof).
• All generic immunosuppressants and the brand will be bioequivalent to each other as confirmed in in vitro dissolution studies.
• Tacrolimus metabolism and clearance will not be affected by the formulation.
• Alternative bioequivalence metrics such as using narrower acceptance intervals and a population pharmacokinetic approach will confirm bioequivalence among the brand and the six generics in the aforementioned high-risk transplant patient populations.

To test these hypotheses, we propose the following four Aims:

AIM 1: Using a retrospective cohort design, we will evaluate the clinical and safety outcomes among adult transplant recipients whose tacrolimus dosage was converted from Prograf® to a generic formulation.

In a retrospective review, evaluate the impact of generic conversion in adult transplant recipients on post transplant outcomes one year prior to conversion to one year post conversion. Variables for analysis will include but not limited to incidence of rejection, hospital admission, changes in renal function, changes in transplanted organ function. All tacrolimus levels and dose changes during this period will be collected and compared. Additional pharmacokinetic modeling of this data will be performed for comparison.

Aim 2: Identification of a single lot with the longest expiration date from each unique manufactured product approved in the United States and conduct systematic dissolution, content uniformity and purity testing on all tacrolimus product.

We will conduct systematic dissolution testing of the brand and all currently approved tacrolimus drug formulations using the FDA-recommended dissolution method. We propose to test and compare the 1 mg capsule strength. In addition, we will compare the different formulations in terms of potency, purity and other quality attributes. This work will be carried out in the GMP-compliant facilities of The University of Iowa Pharmaceuticals (uip.pharmacy.uiowa.edu) and at the University of Colorado (iC42 Clinical Research and Development, Department of Anesthesiology, University of Colorado, Laboratory Director: U. Christians). Based on these studies, if all lots pass current USP standards, we will proceed to the clinical trial described in Aim 3.

Aim 3: Comparison of the relative bioavailability and steady-state pharmacokinetics of 6 tacrolimus formulations in a prospective, 6-way cross-over study including CYP3A5 expressors (n=30) and non-expressor (n=30) transplant patients. Six tacrolimus formulations will be tested and each patient will receive each formulation once. As we proposed to test bioequivalence in the steady-state, patients will receive the test formulations for one week prior to pharmacokinetic evaluation. The pharmacokinetic evaluation will incorporate limited sampling strategies with a focus on fully characterizing the Cmax out to hour 4 post dose. Subsequent PK sampling and trough blood concentrations will be monitored on a daily basis using dried blood spots that the study subjects will collect by themselves at home. The daily monitoring of levels will allow us to specifically address whether the need of additional monitoring upon formulation conversion is necessary. It will be critical that the patients are adherent to their test medication to ensure that they have reached steady state. This will be monitored using test diaries, pill counts and MEMS caps (Medication Event Monitoring System (MEMS), AARDEX Corp, Palo Alto, CABioequivalence will be tested using scaled average bioequivalence metrics and analysis of variance as appropriate and intra-individual variability of the formulations will be compared. This will also include the analysis of potential period and sequence effects. A combination of limited sampling strategy and dry spot analysis in combination with population pharmacokinetic modeling will be utilized to fully characterize the PK profile of these formulations. In addition, the same study will be conducted in 36 pediatric patients.

Aim 4. Subgroup analysis, population pharmacokinetics, and average bioequivalence Aim 4 is an exploratory aim in which we will (A) address the concern that bioequivalence in the "general" patient population will not translate to special subgroups such as high risk transplant recipients as characterized by genotype, race, age, gender, sensitization (repeat transplant or cytotoxic PRA >35% or calculated PRA >50%), presence of concomitant steroids, presence of diabetes. and (B) test alternative bioequivalence metrics that have been proposed for the analysis for immunosuppressant generics such as narrower acceptance intervals, average bioequivalence was well as population pharmacokinetics.