Hepatic Disposition and Metabolite Kinetics of a Homologous Series of Diflunisal Esters

Abstract

The hepatic disposition and metabolite kinetics of a homologous series of diflunisal O–acyl esters (acetyl, butanoyl, pentanoyl, and hexanoyl) were determined using a single–pass perfused in situ rat liver preparation. The experiments were conducted using 2% BSA Krebs–Henseleit buffer (pH7.4), and perfusions were performed at 30mL/min in each liver. O-Acyl esters of diflunisal and pregenerated diflunisal were injected separately into the portal vein. The venous outflow samples containing the esters and metabolite diflunisal were analyzed by high performance liquid chromatography (HPLC). The normalized outflow concentration–time profiles for each parent ester and the formed metabolite, diflunisal, were analyzed using statistical moments analysis and the two–compartment dispersion model. Data (presented as mean±standard error for triplicate experiments) was compared using ANOVA repeated measures, significance level P<0.05. The hepatic availability (AUC′), the fraction of the injected dose recovered in the outflowing perfusate, for O-acetyldiflunisal (C2D=0.21±0.03) was significantly lower than the other esters (0.34–0.38). However, RN/fu, the removal efficiency number RN divided by the unbound fraction in perfusate fu, which represents the removal efficiency of unbound ester by the liver, was significantly higher for the most lipophilic ester (O-hexanoyldiflunisal, C6D=16.50±0.22) compared to the other members of the series (9.57 to 11.17). The most lipophilic ester, C6D, had the largest permeability surface area (PS) product (94.52±38.20mLmin–1 g–1 liver) and tissue distribution value VT (35.62±11.33mLg–1 liver) in this series. The MTT of these O-acyl esters of diflunisal were not significantly different from one another. However, the metabolite diflunisal MTTs tended to increase with the increase in the parent ester lipophilicity (11.41±2.19s for C2D to 38.63±9.81s for C6D). The two-compartment dispersion model equations adequately described the outflow profiles for the parent esters and the metabolite diflunisal formed from the O-acyl esters of diflunisal in the liver.