Oxfendazole is a broad spectrum benzimidazole anthelmintic approved
for veterinary use. It is effective to protect livestock and poultry
from most of the parasites such as roundworms, tapeworms, strongyles
and pinworms. The drug is mainly applied in the form of pills,
tables, drenches and bolus, etc. especially for horses, goats,
cattle, sheep, etc.
The drug functions on parasites by binding to tubulin, which is a
structural protein of microtubules. In the parasites the blocking of
microtubules interferes with the uptake of glucose, which ultimately
empties the glycogen reserves. This blocks the whole energy
management mechanism of the parasites and eventually leads to death.
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A metabolite of Fenbendazole (F246750).
ChEBI: A member of the class of benzimidazoles that is fenbendazole in which the sulfur has been oxidised to the corresponding sulfoxide.
5.0 g of 2-amino-4-chloro-1-nitrobenzene is added to a solution of sodium phenyl mercaptide, prepared under nitrogen from 2.53 g 57% sodium hydride and 6.2 ml thiophenol in 20 ml dimethylformamide, with a 10 ml dimethylformamide rinse. The mixture is stirred under nitrogen for 3 h at 20°30°C and then diluted with water. The crude product is washed with water and hexane, then recrystallized from methanol, yielding 2-amino-4-phenylthio-1nitrobenzene.
6.0 g of 2-amino-4-phenylthio-1-nitrobenzene is dissolved in 80 ml acetic anhydride and treated with a few drops of sulfuric acid. The mixture is left at 20°-30°C for 2 h then a little sodium acetate added and the solvent removed under vacuum. The residue is treated with water, filtered and recrystallized from methanol yielding 2-acetamido-4-phenylthio-1-nitrobenzene.
7.0 g of 2-acetamido-4-phenylthio-1-nitrobenzene is dissolved in 70 ml chloroform and treated, at -20°C to -15°C, with a solution of 5.0 g 40% peracetic acid in 10 ml methanol. The mixture is allowed to warm slowly to 20°C and stirred for 4 h. The reaction mixture is extracted with sodium bisulfite solution, then sodium bicarbonate solution, dried and evaporated. The residual gum of 2-acetamido-4-phenylsulfinyl-1-nitrobenzene is treated with 20 ml 5 N sodium hydroxide and 40 ml methanol at 20°-25°C for 1 h. Water is then added and essentially pure 2-amino-4-phenyl-sulfinyl-1-nitrobenzene filtered off. Recrystallization may be effected from benzene.
5.4 g of 2-amino-4-phenylsulfinyl-1-nitrobenzene is hydrogenated at 1 atmosphere pressure in 500 ml methanol in the presence of 5.0 g 5% palladized carbon, until the theoretical uptake of hydrogen has occurred. The catalyst is removed by filtration and the filtrate stripped under vacuum. The residue is recrystallized from methanol-benzene, yielding 1,2-diamino-4phenylsulfinylbenzene.
A mixture of 5.5 g of 1,2-diamino-4-phenylsulfinylbenzene, 4.3 g of 1,3-bismethoxycarbonyl-S-methylisothiourea and 1.2 ml acetic acid in 100 ml
ethanol and 100 ml water is refluxed for 4 h. The mixture is cooled and essentially pure 6-phenylsulfinyl-2-carbomethoxyaminobenzimidazole filtered off and washed with methanol. Recrystallization may be effected from methanol-chloroform (melting point 253°C, dec.).
Synanthic Veterinary (Syntex).
Experimental reproductive effects. Human mutation data reported. Whenheated to decomposition it emits toxic fumes of SOx and NOx.
Veterinary Drugs and Treatments
Oxfendazole (Synanthic) is indicated in cattle for the removal and
control of lungworms, roundworms (including inhibited forms of
Ostertagia ostertagi) and tapeworms.
Oxfendazole as Benzelmin was indicated (no longer marketed
in the USA) for the removal of the following parasites in horses:
large roundworms (Parascaris equorum), large strongyles (S. edentatus,
S. equinus, S. vulgaris), small strongyles, and pinworms
(Oxyuris equi).
Oxfendazole has also been used extra-label in sheep, goats, and
swine; see Dosage section for more information.
[1] Patent: US4792610, 1988, A
