Pharmacologic interaction between oxfendazole and triclabendazole: In vitro biotransformation and systemic exposure in sheep.

The aim of the current work was to evaluate a potential pharmacokinetic interaction between the flukicide triclabendazole (TCBZ) and the broad-spectrum benzimidazole (BZD) anthelmintic oxfendazole (OFZ) in sheep. To this end, both an in vitro assay in microsomal fractions and an in vivo trial in lambs parasitized with Haemonchus contortus resistant to OFZ and its reduced derivative fenbendazole (FBZ) were carried out. Sheep microsomal fractions were incubated together with OFZ, FBZ, TCBZ, or a combination of either FBZ and TCBZ or OFZ and TCBZ. OFZ production was significantly diminished upon coincubation of FBZ and TCBZ, whereas neither FBZ nor OFZ affected the S-oxidation of TCBZ towards its sulfoxide and sulfone metabolites. For the in vivo trial, lambs were treated with OFZ (Vermox® oral drench at a single dose of 5 mg/kg PO), TCBZ (Fasinex® oral drench at a single dose of 12 mg/kg PO) or both compounds at a single dose of 5 (Vermox®) and 12 mg/kg (Fasinex®) PO. Blood samples were taken to quantify drug and metabolite concentrations, and pharmacokinetic parameters were calculated by means of non-compartmental analysis. Results showed that the pharmacokinetic parameters of active molecules and metabolites were not significantly altered upon coadministration. The sole exception was the increase in the mean residence time (MRT) of OFZ and FBZ sulfone upon coadministration, with no significant changes in the remaining pharmacokinetic parameters. This research is a further contribution to the study of metabolic drug-drug interactions that may affect anthelmintic efficacies in ruminants.

Total determination of triclabendazole and its metabolites in bovine tissues using liquid chromatography-tandem mass spectrometry.

A reliable LC-MS/MS analytical method for the determination of residual triclabendazole and its principal metabolites (triclabendazole sulfoxide, triclabendazole sulfone and keto-triclabendazole) in bovine tissues was developed, in which triclabendazole and its metabolites are oxidized to keto-triclabendazole as a marker residue. The method involves sample digestion with hot sodium hydroxide, thus releasing the bound residues of various triclabendazole metabolites in bovine tissues. The target compounds are extracted from the digest mixture with ethyl acetate, defatted by liquid-liquid partitioning using n-hexane and acetonitrile, then oxidized with hydrogen peroxide in a mixture of ethanol and acetic acid. The reaction mixture is cleaned up using a strong cation exchange cartridge (Oasis MCX) and the analytes are quantified using LC-MS/MS. The optimal conditions for the complete oxidation of triclabendazole and its metabolites to keto-triclabendazole are an incubation time of 16 h and a temperature of 90 °C. The developed method was evaluated using three bovine samples: muscle, fat, and liver. Samples were spiked with triclabendazole and its principal metabolites at 0.01 mg/kg and at the Japanese Maximum Residue Limits (MRLs) established for each sample. The validation results show excellent recoveries (81-102%) and precision (<10%) for all target compounds. The limit of quantification (S/N ≥ 10) of the developed method is 0.01 mg/kg. These results suggest the developed method is applicable to quantifying residual triclabendazole in bovine tissues in compliance with the MRLs established by the Codex Alimentarius and EU and Japanese regulations, and thus the proposed method will be a useful tool for the regulatory monitoring of residual triclabendazole and its metabolites.