An examination of the potential effect of lipids on the first‐pass metabolism of the lipophilic drug anethol trithione

In this study, an examination of the potential effect of lipids on the first‐pass metabolism of anethol trithione (ATT) was investigated. ATT is metabolized rapidly and extensively in liver into 4‐hydroxy‐anethole trithione (ATX), which was confirmed using the rat intestinal perfusion with the mesenteric cannulation model. Male Sprague-Dawley rats were orally administered of the lipid‐based formulations (prepared by medium chain triglycerides (MCT)), the cyclodextrin formulation and the suspension formulation, respectively. For 6.75 mg/kg groups, ATX/ATT area under the plasma concentration‐time curve (AUC) ratio decreased by 87% and 76% after administration of the MCT‐based formulations and the cyclodextrin formulation, when compared with the suspension formulation (p < 0.05), respectively; for 2.25 mg/kg groups, it decreased by 53% in the MCT group when compared with the cyclodextrin group (p < 0.05). The saturation of pre‐system metabolism of ATT was observed after administration of the MCT‐based formulations and the cyclodextrin formulation, likely as a result of enhanced absorption and therefore presentation of higher drug concentrations to liver, when compared with the suspension formulation. A trend toward lower systemic metabolite to parent ratios was evident after administration of the lipid formulations, when compared with the cyclodextrin formulation; however, this was not statistically significant. Further studies on the potential for lipids to inhibit hepatic metabolism are therefore warranted. © 2011 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:5048-5058, 2011