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ALBENDAZOLE: Safety Summary for Veterinary Use

WHO Acute Hazard classification: Not listed.


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.


Acute Toxicity and Tolerance of Albendazole

  • LD50 acute, rats, p.o 1.55 to 3.25 g/kg
  • LD50 acute, cattle, p.o. 300 mg/kg
  • LD50 acute, sheep, p.o. 200 mg/kg
  • Safety margins:
    • Cattle 7,5 - 10; tolerate up to 45 mg/kg without symptoms (usual therapeutic dose is 5 to 10 mg/kg)
    • Sheep: 5 - 10; tolerate 40 to 100 mg/kg without symptoms (usual therapeutic dose is 5 to 10 mg/kg)
  • Dogs: NEL (no effect level) in 1-year chronic toxicity studies was 0.35 mg/kg/day p.o.
  • Dogs: treatment against Giardia (25 mg/kg 2x/day, 5 days, followed by 50 mg/kg 2x/day, 5 days) caused reversible pancytopenia (reduced number of white and red blood cells) due to damage to the bone marrow. 
  • Cats: treatment against Paragonimus (25 mg/kg 2x/day, 4 days) caused reversible pancytopenia, and in some cases lethargy and depression.
  • Alpacas: oral treatment ar 19 mg/kg during 5 days caused toxic symptoms (aqueous diarrhea, dehydration and leukopenia) resulting in death in spite of intensive therapy.

Toxic Symptoms caused by Albendazole Poisoning

  • Liver, testicles and gastrointestinal tract are the most affected organs after exposure to high albendazole doses.
  • Overdosing may also produce lethargy, loss of appetite, intestinal cramps, nausea, diarrhea and vomiting.
  • Other reported symptoms include dizziness, convulsions and sleeplessness.

Albendazole Side Effects, Adverse Drug Reactions (ADRs) and Warnings

  • Albendazole can have teratogenic effects, particularly in cattle and sheep and shall not be administered to pregnant animals.
  • In pregnant bitches, albendazole treatment can cause reduced weight of puppies at birth and palatoschisis (cleft palate).
  • In birds albendazole treatment can reduce de laying performance and egg hatching.
  • Albendazole should not be administered to animals suffering from hepatic disorders.
  • Never use tablets (or suspensions, pastes, etc.) for dogs in cats, or tablets for large dogs in small dogs. It happens that some users want to save money buying large tablets for treating smaller dogs (or even cats!) twice or more times. The risk of overdosing is considerable, either due to erroneous calculations or to unskilled manipulation. In addition, dog medicines may sometimes contain ingredients that are toxic to cats.
  • Unless prescribed by a veterinary doctor, never use in dogs or cats products for livestock that are not explicitly approved for such use. There is a high risk of overdosing or of adverse drug reactions due to ingredients that are not tolerated by pets or are even toxic to them.

Antidote and Treatment of Albendazole Intoxication

  • There is no specific antidote for albendazole.
  • Treatment consists in supportive and symptomatic measures.
  • After oral intoxication gastric lavage is recommended, as well as administration of active charcoal.

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 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 (incl. dogs and cats).

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.


Environmental Toxicity of Albendazole

  • Not being used in crop pesticides or in public hygiene, knowledge on its environmental fate and impact is very scarce.
  • Nevertheless, it can be assumed that correctly used in dogs, cats and livestock albendazole is unlikely to be detrimental for the environment, including coprophagous insects.

Additional information

Click here for a list and overview of all safety summaries of antiparasitic active ingredients in this site.

  • Albendazole belongs to the chemical class of the benzimidazoles.
  • Albendazole is used in human medicines.
  • Albendazole is not used in crop pesticides.
  • Albendazole is not used in public or domestic hygiene as a biocide.
  • Click here for General safety of antiparasitics for domestic animals.
  • Click here for General safety of antiparasitics for humans.
  • Click here for General safety of antiparasitics for the environment.
  • Click here for technical and commercial information on albendazole.

WARNING

If you intend to use a veterinary drug containing this active ingredient you must carefully read and follow the safety instructions in the product label.  Always ask your veterinary doctor, or pharmacist, or contact the manufacturer. Be aware that the safety instructions for the same veterinary medicine may vary from country to country.

The information in this page must not be confused with the Materials and Safety Datasheets (MSDS) officially issued by manufacturers for active ingredients and many other chemicals. MSDSs target safety during manufacturing, transport, storage and handling of such materials. This safety summary is a complement to the information on product labels and MSDS.

The toxicity of an active ingredient must not be confused with the toxicity of finished products, in this case parasiticidal drugs or pesticides. Finished products contain one or more active ingredients, but also other ingredients that can be relevant from the safety point of view.

All information in this site is made available in good faith and following a reasonable effort to ensure its correctness and actuality. Nevertheless, no this regarding guarantee is given, and any liability on its accuracy, integrity, sufficiency, actuality and opportunity is denied. Liability is also denied for any possible damage or harm to persons, animals or any other goods that could follow the transmission or use of the information, data or recommendations in this site by any site visitor or third parties.

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