Albendazole is a broad-spectrum antiparasitic active ingredient used in veterinary and human medicine. It is used in pets and livestock against internal parasites (roundworms, tapeworms, and liver flukes). It is not used against agricultural and household pests. It belongs to the chemical class of the benzimidazoles.
EFFICACY AGAINST PARASITES
Type of action: broad-spectrum nematicide, taenicide and flukicide anthelmintic, endoparasiticide
Main veterinary parasites controlled: gastrointestinal and respiratory roundworms (= nematodes), tapeworms and adult liver flukes
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 albendazole used in domestic animals.
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Oral LD50, rat, acute*: 1500 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.
WARNING: Albendazole, as well as ricobendazole, parbendazole and cambendazole can be teratogenic and should not be administered to pregnant females.
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 albendazole safety (poisoning, intoxication, overdose, antidote, symptoms, etc.).
General safety information for 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: Smith-Kline ( → PFIZER → ZOETIS)
Some original brands: VALBAZEN
Patent: Expired (particular formulations may be still patent-protected)
Use in LIVESTOCK: Yes, massive
Use in HORSES: Yes, scarce
Use in DOGS and CATS: Yes, abundant
Main delivery forms:
Use in human medicine: Yes
Use in public/domestic hygiene: No
Use in agriculture: No
Generics available: Yes, numberless
In livestock & HORSES: Yes, as all benzimidazoles, very frequent worldwide in gastrointestinal roundworms in sheep, goats, cattle & horses. Less frequent but increasing and spreading in liver flukes (Fasciola hepatica) also in sheep, goats and cattle.
In dogs and cats: No
Albendazole is a veteran anthelmintic (wormer) compound belonging to the chemical class of the benzimidazoles. Albendazole is one of the generic anthelmintics most used on livestock worldwide. There are hundreds of brands.
For livestock it is available in the form of drenches, feed additives, bolus, tablets, pills, etc and slow-release devices, all for oral administration. There are no classic injectables or pour-ons with albendazole, excepting some drenches that are approved for intraruminal injection in some countries. Albendazole sulfoxide, also known as ricobendazole is available in some countries as an injectable.
Both for livestock and pets it is very often used in combinations that broaden the spectrum of activity. Typical mixtures for livestock include a flukicide (e.g. triclabendazole, closantel, etc.) and/or a macrocyclic lactone (typically ivermectin) and/or levamisole. For dogs and cats it is mostly combined with a taenicide (e.g. praziquantel).
Albendazole was approved for use as a human medicine in 1987. Interestingly, it is one of the few medicines that were first introduced for animals and only later for humans. Another classic example is ivermectin.
Efficacy of albendazole
Albendazole is the benzimidazole with the broadest spectrum of efficacy. It is effective 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 arrested larvae of several species. It is also effective against most livestock tapeworms (e.g. Moniezia, Taenia) and against adult liver flukes (Fasciola hepatica and Fascioloides magna), but not against immature stages. As other benzimidazoles albendazole has no efficacy whatsoever against external parasites (ticks, flies, lice, mites, etc).
In horses it controls the major parasitic roundworms such as Large Strongyles (Cyathostomins), Small Strongyles (Strongylus spp), Parascaris equorum, etc. as well as tapeworms. (e.g. Anaplocephala spp).
It is also effective against the major parasitic roundworms (e.g. Ancylostoma, Toxocara, Trichuris, Uncinaria) and tapeworms (e.g. Echinococcus, Dipylidium, Taenia, etc.) of dogs and cats, as well as against giardiasis (beaver fever), a parasitic infection caused by Giardia spp, a protozoan parasite of animals and humans.
In ruminants, unless delivered using a slow-release device, albendazole 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 days, but not for weeks. In non-ruminants the residual effect is substantially shorter, i.e. only a few hours.
Albendazole has no efficacy whatsoever against external parasites.
Unfortunately, resistance of several gastrointestinal roundworms to all benzimidazoles, including albendazole is already very high and very frequent worldwide in sheep and goats, slightly lower in cattle. Resistance of the liver fluke (Fasciola hepatica) is not that dramatic, but is spreading in several countries. For this reason, the risk that benzimidazoles fail to protect ruminants against gastrointestinal roundworms is considerable worldwide.
Worm resistance to benzimidazoles in dogs, cats, pig and poultry are so far not a serious problem.
Pharmacokinetics of albendazole
After oral administration of albendazole, up to 45% of the administered dose is absorbed into the bloodstream. In ruminants, the slow passage through the complex stomach prolongs the time it can be absorbed. Direct administration into the abomasum (e.g. due to the "oesophageal groove reflex") strongly diminishes the absorption and consequently its efficacy.
Absorbed albendazole is very quickly metabolized in the liver to its sulfoxide derivative, which has also anthelmintic efficacy and is exactly ricobendazole, another commercial anthelmintic active ingredient. In fact, in most species the parent molecule remains almost undetectable in blood after administration. In a second much slower step the sulfoxide is further metabolized in the liver to the sulfone metabolite that has no anthelmintic efficacy. The high plasma levels of albendazole sulfoxide make it effective against adult worms and immature stages in various host tissues and organs outside the gastrointestinal tract.
Interestingly, part of the sulfoxide produced through metabolism is released back to the rumen, where the bacterial flora reduces it back to albendazole. This increases the bioavailability of albendazole in ruminants.
Excretion occurs through bile and feces, as well as through urine. In ruminants 60-70% of the administered dose is excreted through urine in the form of various metabolites, the major one being the sulfoxide. In sheep about 14% of the administered dose is excreted through the bile, partly in the form of various active metabolites, which enables reaching effective anthelmintic concentrations in the bile ducts.
In dogs, cats and birds, the absence of such a rumen reservoir as in ruminants strongly shortens the residual effect, which may require a higher dose or more frequent treatments to achieve the desired efficacy. In sheep and goats albendazole sulfoxide remains detectable in plasma for about 3 days, in dogs for less than 12 hours.
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 is absorbed. Consequently it is advisable to reduce the animals' access to feed (especially to fresh pasture, not to water) 24-36 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 albendazole.
In contrast with this, administration of albendazole with the food increases its bioavailability in carnivores.
Influence of parasites. Heavy infestations with gastrointestinal roundworms reduce the bioavailability of albendazole 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 albendazole 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.
Mechanism of action of albendazole
The molecular mode of action of all benzimidazoles, including albendazole, 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.
Albendazole also inhibits a helminth-specific fumarate reductase, an enzyme involved in the energy management of the worm cells as well.
Click here to view the list of all technical summaries of antiparasitic active ingredients in this site.