AIMS: To assess the comparative drug systemic exposure of a reference (RF) and four test (Test I, Test II, Test III and Test IV) formulations of triclabendazole (TCBZ) in heifers. METHODS: Thirty Holstein heifers were randomly distributed into five groups (n=6 per group). Animals in the RF group received the reference formulation (Fasinex), and those in the other groups received different commercially available TCBZ formulations (Test I, Test II, Test III and Test IV). All treatments were orally administered at 12 mg/kg bodyweight. The concentrations of TCBZ metabolites in plasma between 0 and 168 hours after treatment were quantified by high-performance liquid chromatography (HPLC). RESULTS: Triclabendazole sulphoxide (TCBZ.SO) and TCBZ-sulphone (TCBZ.SO2) were the only analytes recovered in plasma. Only the Test I formulation did not differ from the RF for all pharmacokinetic paramet...