WHO Acute Hazard classification: Not listed.

Mechanism of action of Flubendazole

The molecular mode of action of all benzimidazoles, including flubendazole, 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.

Acute Toxicity and Tolerance of Flubendazole

  • LD50 acute, rats, p.o.  >5000 mg/kg
  • LD50 acute, mice, p.o.  >5000 mg/kg
  • LD50 acute, chicken, p.o.  >640 mg/kg
  • Safety margin in swine >20
  • In dogs, daily doses of 10 and 40 mg/kg 6 days a week during 3 weeks prostatic hypoplasia (reduced development) and congestion of cauda of the epididymis were observed in all males.
  • Broiler breeder pullets treated with flubendazole at 60, 80 and 120 mg/kg mixed in the feed during 7 days showed no toxic symptoms, excepting a lower hematocrit value and lower red cell count in the highest-dose group.
  • In pregnant sows treated at 8 mg/kg/day mixed in the feed from the day of mating after farrowing no significant abnormalities were found in the born piglets. The same was found after treatment at 50 mg/kg/day mixed in the feed from the day of mating until day 70 of pregnancy.
  • As a general rule dogs, cats and livestock tolerate flubendazole very well, usually without adverse drug reactions.

Toxic Symptoms caused by Flubendazole Poisoning

  • As a general rule, poisoning with flubendazole is quite unusual, due to its low toxicity, the high safety margins and the fact that most species tolerate it very well.

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

  • Flubendazole should not be used in pregnant or lactating queens, nor in puppies younger than 1 year destined to reproduction.
  • After injection of flubendazole solved in sodium citrate a whitish viscous deposit was observed at the injection site.
  • 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 Flubendazole Intoxication

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

Pharmacokinetics of Flubendazole

Flubendazole is almost insoluble in water. Orally administered flubendazole is poorly absorbed into the bloodstream. This means that significant amounts remain in the gastrointestinal tract and are available for the control of gut-dwelling roundworms and tapeworms. But blood levels are low and efficacy against tissue-dwelling worms may be lower or insufficient.

Absorbed flubendazole is quickly broken down in the liver to metabolites without anthelmintic efficacy. Both the parent molecule and its metabolites are excreted mainly through bile and feces, the rest through urine. However, there are important species-specific differences.

In dogs about 90% of the administered dose was excreted in the first 4 days after treatment, >80% through feces, most of it as unchanged flubendazole. About 6% was excreted through urine, most of it as various metabolites.

In pigs fed flubendazole during 5 days, ~80% of the administered dose was excreted within 30 days after end of the medication period. About 55% was excreted in feces and ~25% in urine.

In layers, flubendazole leaves very low residues in eggs, which allows low or nil withholding periods for eggs.

Environmental Toxicity of Flubendazole

  • 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 flubendazole 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.

  • Flubendazole belongs to the chemical class of the benzimidazoles.
  • Flubendazole is used in human medicines.
  • Flubendazole is not used in crop pesticides.
  • Flubendazole 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 flubendazole.


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.