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.