Adverse reactions (frequency and seriousness): None known.
Use during pregnancy, lactation or lay:
Laying birds:
Chickens: can be used during lay. See also section 4.10 ‘Overdose (symptoms, emergency procedures), if necessary’.
Fertility:
Chickens: the safety of the veterinary medicinal product has not been established in male birds. Therefore use in male birds only according to the benefit/risk assessment by the responsible veterinarian.
Pheasants: the safety of the veterinary medicinal product has not been evaluated in breeding pheasants. Therefore in these birds use only according to the benefit/risk assessment by the responsible veterinarian.
Interaction with other medicinal products and other forms of interaction: None known.
In the absence of compatibility studies, this veterinary medicinal product must not be mixed with other veterinary medicinal products.
Overdose (symptoms, emergency procedures, antidotes), if necessary
No adverse reactions have been observed at up to 6.7-fold the maximum recommended dose of 3 mg/kg body weight/day over 30 days in broilers (aged approximately 14 days) and up to a 40-fold overdose in pheasants (aged approximately 3 weeks).
No adverse reactions have been observed in layers and breeders administered a dose rate of 4-fold the maximum recommended dose of 3 mg/kg body weight/day (i.e., 12 mg/kg body weight/day) over 30 days, however offspring viability (including reduced incubation survival, reduced fertility (fewer eggs hatched) and lower body weight of chicks) was adversely affected at this dose rate.
Increased frequency of physical abnormalities of eggs was observed at dose rates of 3- and 4-fold the maximum recommended dose of 3 mg/kg body weight/day administered over 30 days.
No adverse effects on offspring viability or egg physical characteristics were observed at 2-fold the maximum recommended dose of 3 mg/kg/day (chickens) over 30 days in layers and breeders.
Pharmacotherapeutic group: Anthelmintics, benzimidazole derivatives – fenbendazole.
ATCvet Code: QP52AC13
Pharmacodynamic properties
Fenbendazole is an anthelmintic belonging to the benzimidazole-carbamate group. It acts by interfering with the energy metabolism of the nematode or cestode.
Fenbendazole inhibits the polymerisation of tubulin to microtubules. This interferes with essential structural and functional properties of the cells of helminths, such as formation of the cytoskeleton, formation of the mitotic spindle and the uptake and intracellular transport of nutrients and metabolic products. Fenbendazole is active and has a dose dependent activity on Heterakis gallinarum (adult stages), Ascaridia galli (adult stages), Capillaria obsignata (adult stages) and Raillietina echinobothrida (adult stages) in chickens, and activity against adult Heterakis gallinarum in pheasants.
Pharmacokinetic particulars
After oral administration fenbendazole is only partially absorbed. Following absorption, fenbendazole is rapidly metabolised in the liver mainly to its sulphoxide (oxfendazole) and further to its sulphone (oxfendazole sulphone). In chickens oxfendazole sulfone is the maincomponent detected in plasma, accounting for about 3/4 of the total AUC (i.e. the sum of the AUC for fenbendazole, oxfendazole and oxfendazole sulphone). Fenbendazole and its metabolites are distributed throughout the body, reaching highest concentrations in the liver.
The elimination of fenbendazole and its metabolites occurs primarily via the faeces.