Pharmacokinetics of Intragastric Ursodeoxycholic Acid and Its Impact on Bile Acid Profiles in Horses

Ursodeoxycholic acid (UDCA), a secondary bile acid (BA) with therapeutic applications, is standard therapy for cholestatic hepatopathies in humans. In recent years, its use has been increasingly explored in equine medicine for similar indications. Pharmacokinetic data for UDCA in horses are currently lacking. This study aimed to describe the pharmacokinetic parameters following a single intragastric administration of 15 mg/kg in nine healthy, fasted horses and to characterize the changes in their BA profiles. Plasma concentrations of UDCA were measured at specific time points using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Pharmacokinetic analysis revealed a sharp increase in plasma concentrations within the first 1-3 h, with peak concentrations (Tmax) occurring at 2.44 ± 1.3 h. Plasma concentrations decreased significantly in most horses at 24 h, with negligible concentrations detected at 48-72 h. Mean half-life was calculated at 7.99 ± 2.25 h, and the dose interval estimate mean was 24.29 h. BA profile analysis demonstrated an increase in total BA concentrations post-administration, with a notable rise in the percentage of UDCA relative to other BAs. Based on these findings, we conclude that the intragastric dose of 15 mg/kg every 24 h is appropriate for horses. Clinicians should be aware that, post-administration, total BA concentrations are likely to increase within hours, with UDCA becoming the predominant BA.