Anthelmintics, benzimidazole derivatives – fenbendazole.
ATCvet Code: QP52AC13
Pharmacodynamic properties
Fenbendazole is an anthelmintic belonging to the benzimidazole-carbamate group. It acts by binding to beta-tubulin, thereby inhibiting the polymerisation of tubulin to microtubules and subsequently interfering with energy metabolism.
The anthelmintic affects both adult and immature stages of Ascaris suum.
Pharmacokinetic properties
Fenbendazole is only partly absorbed after oral administration and is then metabolised in the liver. Body clearance of fenbendazole in serum after intravenous administration to pigs at a dose rate of 1 mg/kg was 1.36 L/h/kg, volume of distribution at steady state was 3.35 L/kg and the mean residence time was 2.63 hours. After oral administration at a dose rate of 5 mg/kg the peak plasma concentration of fenbendazole was 0.07µg/ml, the Tmax was 3.75 hours and the mean residence time was 15.15 hours. The bioavailability was 27.1 %. Oxfendazole was the major plasma metabolite i.e 2/3 of the total AUC.
Fenbendazole and its metabolites are distributed throughout the body and high concentrations can be found in the liver.
The elimination of fenbendazole and its metabolites occurs primarily via the faeces (>90%) and to a small extent in the urine and milk.
Fenbendazole is metabolised to its sulphoxide, then to sulphone and amines.