Development of 4‐Pyridoxic Acid PBPK Model to Support Biomarker‐Informed Evaluation of OAT1/3 Inhibition and Effect of Chronic Kidney Disease

Abstract

Monitoring endogenous biomarkers is increasingly used to evaluate transporter‐mediated drug–drug interactions (DDIs) in early drug development and may be applied to elucidate changes in transporter activity in disease. 4‐pyridoxic acid (PDA) has been identified as the most sensitive plasma endogenous biomarker of renal organic anion transporters (OAT1/3). Increase in PDA baseline concentrations was observed after administration of probenecid, a strong clinical inhibitor of OAT1/3 and also in patients with chronic kidney disease (CKD). The aim of this study was to develop and verify a physiologically‐based pharmacokinetic (PBPK) model of PDA, to predict the magnitude of probenecid DDI and predict the CKD‐related changes in PDA baseline. The PBPK model for PDA was first developed in healthy population, building on from previous population pharmacokinetic modeling, and incorporating a mechanistic kidney model to consider OAT1/3‐mediated renal secretion. Probenecid PBPK model was adapted from the Simcyp database and re‐verified to capture its dose‐dependent pharmacokinetics (n = 9 studies). The PBPK model successfully predicted the PDA plasma concentrations, area under the curve, and renal clearance in healthy subjects at baseline and after single/multiple probenecid doses. Prospective simulations in severe CKD predicted successfully the increase in PDA plasma concentration relative to healthy (within 2‐fold of observed data) after accounting for 60% increase in fraction unbound in plasma and additional 50% decline in OAT1/3 activity beyond the decrease in glomerular filtration rate. The verified PDA PBPK model supports future robust evaluation of OAT1/3 DDI in drug development and increases our confidence in predicting exposure and renal secretion in patients with CKD.