Mechanistic modelling of tesaglitazar pharmacokinetic data in subjects with various degrees of renal function--evidence of interconversion.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT Tesaglitazar, is predominantly metabolized (to an acyl glucuronide of the parent compound) and 20% of given dose is found unchanged in the urine. Acyl glucuronides are know to be unstable and can become hydrolysed back to parent compound, a phenomena called interconversion. WHAT THIS STUDY ADDS A likely mechanism (interconversion) for the cause of the increased exposure of tesaglitazar in subjects with impaired renal function. A possible modelling framework to evaluate interconversion without dosing of the metabolite based on the simultaneous analysis of plasma and urine data from a group of subjects with varying renal function. A mechanistic understanding of the pharmacokinetic properties of tesaglitazar and its metabolite. AIMS To develop a mechanistic pharmacokinetic (PK) model for tesaglitazar and its metabolite (an acyl glucuronide) following oral administration of tesaglitazar to subjects with varying renal function, and derive an explanation for the increased plasma exposure of tesaglitazar in subjects with impaired renal function. METHODS Data were from a 6-week study in subjects with renal insufficiency and matched controls undergoing repeated oral dosing with tesaglitazar (n = 41). Compartmental population PK modelling was employed to describe the PK of tesaglitazar and its metabolite, in plasma and urine, simultaneously. Two hypotheses were tested to investigate the increased exposure of tesaglitazar in subjects with renal functional impairment: tesaglitazar metabolism is correlated with renal function, or metabolite elimination is reduced in renal insufficiency, leading to increased hydrolysis (interconversion) to the parent compound via biliary circulation. RESULTS The hypothesis for interconversion was best supported by the data. The population PK model included first-order absorption, two-compartment disposition and separate renal (0.027 l h(-1)) and metabolic (1.9 l h(-1)) clearances for tesaglitazar. The model for the metabolite; one-compartment disposition with renal (saturable, V(max) = 0.19 micromol l(-1) and K(m) = 0.04 micromol l(-1)) and nonrenal clearances (1.2 l h(-1)), biliary secretion (12 h(-1)) to the gut, where interconversion and reabsorption (0.8 h(-1)) of tesaglitazar occurred. CONCLUSION A mechanistic population PK model for tesaglitazar and its metabolite was developed in subjects with varying degrees of renal insufficiency. The model and data give insight into the likely mechanism (interconversion) of the increased tesaglitazar exposure in renally impaired subjects, and separate elimination and interconversion processes without dosing of the metabolite.