The integrated assessment included evaluation of FLBZ and metabolites plasma disposition kinetics, liver metabolism and ex vivo ability to diffuse into the cestode parasite Moniezia benedeni.
In a cross-over kinetic study, six healthy Corriedale sheep were treated with FLBZ by intravenous (i.v.) (4% solution) and intraruminal (i.r.) (4% suspension) administrations at the same dosage (5 mg/kg) with a 21-day washout period between treatments.
Blood samples were collected between 0 and 72 h post-treatments. Sheep liver microsomes were incubated with 40 m FLBZ and specimens of the cestode parasite M. benedeni, collected from untreated animals, were incubated (5120 min) with FLBZ and its reduced (R-FLBZ) metabolite (5 m). Samples of plasma, microsomal incubations and parasite material were prepared and analyzed by high-performance liquid chromatography to measure FLBZ and its metabolites.
FLBZ parent drug showed a fast disposition being detected in the bloodstream up to 36 h after its i.v. administration. Both R-FLBZ and hydrolyzed FLBZ (H-FLBZ) metabolites were recovered in plasma as early as 5 min after the i.v. treatment in sheep.
The plasma AUC ratios for R-FLBZ and FLBZ (AUCR-FLBZ/AUCFLBZ) were 4.07 i.v. and 5.55 i.r., respectively. R-FLBZ achieved a significantly higher (P < 0.01) Cmax value (0.14 g/mL at 17.3 h post-treatment) than that observed for the parent drug FLBZ (0.04 g/mL at 14.4 h post-treatment). Low plasma concentrations of FLBZ parent drug were measured between 6 and 48 h, and only trace concentrations of H-FLBZ were detected during a short period of time after the i.r. treatment.
Consistently, sheep liver microsomes metabolized FLBZ into its reduced metabolite at a rate of 9.46 ± 2.72 nmol/mg/h. Both FLBZ and R-FLBZ demonstrated a similar ability to quickly diffuse through the tegument of the cestode parasite.
The data on FLBZ pharmacological behaviour presented here contribute to evaluate its potential to be developed as an anthelmintic for broad spectrum parasite control in ruminants.
Source: Moreno, L., Alvarez, L., Mottier, L., Virkel, G., Sanchez Bruni, S. & Lanusse, C. (2004)
Integrated pharmacological assessment of flubendazole potential for use in sheep: disposition kinetics, liver metabolism and parasite diffusion ability1. In: Journal of Veterinary Pharmacology & Therapeutics 27 (5), 299-308.
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