Evaluation of Renal Drug Transport in Healthy Volunteers

The process of drug elimination that occurs within the kidneys is complex, and involves filtration, secretion and absorptive mechanisms. Many drugs, metabolites and toxins, including organic anions and cations, rely on renal mechanisms for elimination from the body. Failure to recognize the contribution of renal mechanisms involved in drug elimination during the drug development process can result in drug interactions or toxicity in clinical trials. This is increasingly important due to the use of OAT1 inhibitors such as probenecid that are being used in adjuvant treatment regimens. Thus, in order to more fully understand the effects renal disease, drugs and nephrotoxins on the renal transport pathways of tubular secretion in humans, novel approaches that incorporate both in vitro (experimental) as well as clinical observations (clinical trial), also called in-vitro/in-vivo correlations (IVIVC) need to be developed. These methods can then be used to identify and evaluate specific kidney "probe" drugs that undergo extensive tubular secretion. Such approaches are needed to characterize drug clearance by tubular mechanisms and to identify potentially significant drug-drug interactions prior to exposure to patients in Phase 2 and 3 clinical trials. This investigator-initiated pilot project aims to determine the pharmacokinetics of selected FDA-approved compounds (PAH, iothalamate) for use in IVIVC model development. The proposed research is innovative, because it involves a translational approach to development of an IVIVC model applied to renal drug clearance. It is our expectation that the resultant approach will further our understanding of pharmacogenomics, inter-subject variability and renal drug clearance. This approach will generate important new information regarding in vitro drug-drug interactions in light of many new and potent OAT1 blocking agents being introduced for the treatment of human diseases. In future studies, we hope to fully characterize the effects of diseases such as diabetes, hypertension, and nephropathy on renal drug transport mechanisms using IVIVC models. We expect that results from this NIH-funded study will provide needed preliminary data to design future pharmacogenomic and drug interaction studies in humans.