EFFICACY AGAINST PARASITES
Efficacy against a specific parasite depends on the delivery form and on the dose administered.
Click here for general information on features and characteristics of PARASITICIDES.
Click here to view the article in this site with the most common dosing recommendations for oxfendazole used in domestic animals.
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Oral LD50, rat, acute*: >6400 mg/kg
Dermal LD50, rat, acute*: not found
* These values refer to the active ingredient. Toxicity has to be determined for each formulation as well. Formulations are usually significantly less toxic than the active ingredients.
MRL (maximum residue limit) established for either beef, mutton pork or chicken meat*:
- CODEX: Yes
- EU: Yes
- USA: Yes
- AUS: Yes
* This information is an indicator of the acceptance of an active ingredient by the most influential regulatory bodies for use on livestock.
Withholding periods for meat, milk, eggs, etc. depend on delivery form, dose and national regulations. Check the product label in your country.
Learn more about oxfendazole safety (poisoning, intoxication, overdose, antidote, symptoms, etc.).
General information on the safety of veterinary antiparasitics is available in specific articles in this site (click to visit):
- General safety of antiparasitics for domestic animals
- General safety of antiparasitics for humans
- General safety of antiparasitics for the environment
Never use products for livestock on dogs and cats unless they are explicitly approved for both livestock and pets. Pets may not tolerate livestock formulations
It is obvious that veterinary products are not intended for and should never be used on humans!!!
MARKETING & USAGE
Decade of introduction: 1970
Introduced by: WELLCOME, SYNTEX
Some original brands: SYNANTHIC, SYSTAMEX
Patent: Expired (particular formulations may be still patent-protected)
Use on LIVESTOCK: Yes, scarce, mainly in ruminants
Use on HORSES: Yes, scarce
Use on DOGS and CATS: Yes, very scarce
Main delivery forms:
Use in human medicine: No
Use in public/domestic hygiene: No
Use in agriculture: No
Generics available: Yes, rather few
Oxfendazole is a veteran anthelmintic (wormer) compound belonging to the chemical class of the benzimidazoles. Oxfendazole is scarcely used in cattle, sheep, goats and horses, and very scarcely in dogs and cats.
For livestock oxfendazole is available mainly in the form of drenches, bolus, tablets, pills, etc, all for oral administration, mostly alone. Some drenches are also approved for intraruminal injection in several countries. Oxfendazole was used moderately in the past but has been replaced by more effective active ingredients.
For dogs and pets oxfendazole is usually available in the form of drenches.
Efficacy of oxfendazole
Oxfendazole is exactly fenbendazole sulfoxide, i.e. fenbendazole's major metabolite. Both oxfendazole and fenbendazole have the same broad-spectrum of efficacy. They are active against gastrointestinal roundworms and lungworms of livestock, including adults and L4-larvae of the most important species (e.g. of the genus Bunostomum, Haemonchus, Ostertagia - Teladorsagia, Trichostrongylus, Cooperia, Nematodirus, Chabertia, Oesophagostomum, Trichuris, Dictyocaulus, etc.) as well as against arrested larvae of several species. They are also effective against most livestock tapeworms (e.g. Moniezia, Taenia).
In ruminants, unless delivered using a slow-release device, oxfendazole has only a limited residual effect. This means that a single administration will kill the parasites present in the host at the time of treatment and protect against re-infestations for a few more days, but not for weeks or months. In non-ruminants the residual effect is substantially shorter, i.e. only a few hours.
At the therapeutic dose oxfendazole is not effective against flukes and whatsoever external parasites.
Unfortunately, resistance of several gastrointestinal roundworms to all benzimidazoles, including oxfendazole is already very high and very frequent worldwide in sheep and goats, slightly lower in cattle. For this reason, the risk that benzimidazoles fail to protect ruminants against gastrointestinal roundworms is considerable worldwide. Resistance of worms to benzimidazoles in dogs, cats, pig and poultry are so far not a serious problem.
Pharmacokinetics of oxfendazole
In ruminants, oxfendazole is slowly but extensively absorbed to the bloodstream: up to 50% of the administered dose is absorbed. The absorption rate strongly depends on the speed of passage through the rumen: the slower the passage, the higher the absorption. Therefore it is very important that it remains as long as possible in the rumen, to form a reservoir from which it is progressively solved and absorbed. Direct administration or passage into the abomasum (e.g. due to the "oesophageal groove reflex") strongly diminishes the absorption and consequently its efficacy.
Absorbed oxfendazole is well distributed throughout the body, including the lungs and other tissues. Interestingly, absorbed oxfendazole is partly and reversibly reduced to fenbendazole, both in the liver and in the rumen, and vice-versa. However, part of it is irreversibly metabolized to the sulfone derivative that has no anthelmintic efficacy.
In ruminants, parent compound and metabolites are excreted up to 80% through bile and feces, which ensures effective anthelmintic concentration in the gastrointestinal tract for a longer period of time. Excretion through milk is <1% of the administered dose.
Metabolism in cattle and goats is significantly faster than in sheep, which usually requires a higher dose or repeated treatments to achieve the same efficacy.
Influence of diet. In ruminants, reducing the amount of feed slows down the exit flow of the rumen and prolongs the time the anthelmintic remains there and can be absorbed. Consequently it is advisable to reduce the animals' access to feed (especially to fresh pasture, not to water) 24 hours before administration. For the same reason, it is better to keep the animals away from food for about 6 hours after drenching. However sick, weak, or pregnant animals should not be kept away from food and fasting animals should have access to water. In cattle, a fiber-rich diet also increases the bioavailability of oxfendazole.
In contrast with this, in dogs and horses the administration of oxfendazole with the food increases its bioavailability.
Influence of parasites. Heavy infestations with gastrointestinal roundworms reduce the bioavailability of oxfendazole in ruminants. The reason is that the inflamed wall does not properly regulate the pH (acidity) in the abomasum and the intestine, which has a negative influence on the solubility and the absorption of oxfendazole and on the distribution of its metabolites. In addition, the passage of food through the stomach is also faster in case of heavy infestations, which reduces the bioavailability of the anthelmintic. A study in goats showed that an infestation with Ostertagia circumcincta reduced the bioavailability of oxfendazole by ~33%.
Influence of dosing. Splitting the dose in three consecutive daily portions increased the absorption and consequently the bioavailability and the anthelmintic efficacy of oxfendazole in sheep and goats.
Mechanism of action of oxfendazole
The molecular mode of action of all benzimidazoles, including oxfendazole, consists in binding to tubulin, a structural protein of microtubules. These microtubules are important organelles involved in the motility, the division and the secretion processes of cells in all living organisms. In the worms the blocking of microtubules perturbs the uptake of glucose, which eventually empties the glycogen reserves. This blocks the whole energy management mechanism of the worms that are paralyzed and die or are expelled.
Since cell division is also disturbed, worm egg production and development is also blocked by benzimidazoles, i.e. most of them also have an ovicidal effect.
Click here to view the list of all technical summaries of antiparasitic active ingredients in this site.