FORMULATION: «GRANULES» for oral administration, usually mixed with food


CHEMICAL CLASS of the active ingredient(s): BENZIMIDAZOLE


PARASITES CONTROLLED* (spectrum of activity):


Ireland and other countries:

  • 100 mg fenbendazole / kg bw for adult dogs and cats
  • 50 mg fenbendazole / kg for weaned puppies and kittens under 6 months pof age
  • 25 mg fenbendazole / kg for pregnant dogs
  • Frequency of treatment depending on the indication


  • For oral administration only (sprinkled onto food).
  • For the routine treatment of adult dogs and cats: 100 mg fenbendazole/kg bw is recommended.
  • For the treatment of weaned puppies and kittens: 50 mg fenbendazole/kg bw daily for three days is recommended.
  • For the control of lungworm, Oslerus (Filaroides) osleri, in dogs: 50 mg fenbendazole/kg bw per day for 7 days. A repeat course of treatment may be required in some cases.
  • For the control of lungworm, Aelurostrongylus abstrusus, in cats: 20 mg fenbendazole/kg bw per day for five days.
  • For the treatment of pregnant bitches: daily dosage of 25 mg fenbendazole/kg bw from day 40 of pregnancy continuously to 2 days post-whelping.
  • For the treatment of clinical worm infestations in adult dogs and cats: administer 1g Zerofen 22% Granules per 4.4 kg (10 lbs) bw daily for 3 consecutive days (= 50 mg fenbendazole per kg bw daily for 3 days).

* Can be slightly different in some countries: read the product label!


  • LD50 (acute oral) in rats: n.a. for the granules. >10000 mg/kg for fenbendazole a.i.
  • Estimated Hazard Class according to the WHO: not applicable for veterinary medicines

Suspected poisoning? Read the articles on fenbendazole safety in this site.

You may be interested in the following articles in this site dealing with the general safety of veterinary products:


Risk of resistance development? LOW

There are no reports on resistance of dog or cat worms to benzimidazoles about 40 years after their introduction.

Learn more about resistance and how it develops.


Are the active ingredients of this product ORIGINAL* or GENERICS**?

  • Fenbendazole: GENERIC (introduced in the 1970s)

*Meaning that they are still patent protected and generics are not yet available
**Meaning that they have lost patent protection and may be acquired from manufacturers of generic active ingredients other than the holder of the original patent.

COUNTRIES where this product is marketed: Ireland
GENERIC BRANDS available? YES, in most countries. This product itself contains generic fenbendazole.

Click here to learn more about GENERIC vs. ORIGINAL drugs.


ZEROFEN 22% GRANULES is a pet wormer brand from CHANELLE containing generic fenbendazole. It is a generic version of PANACUR C.

Fenbendazole is a veteran benzimidazole introduced in the 1970s (by HOECHST). It is a broad-spectrum anthelmintic effective against most gastrointestinal worms that infect pets, including roundworms (Toxocara canisToxocara cati, Toxascaris leonina), hookworms (Ancylostoma spp, Uncinaria stenocephala) and whipworms (Trichuris vulpis), but also against lungworms (Aelurostrongylus abstrusus) and certain tapeworms (e.g. Taenia spp). It is abundantly used in livestock and horses, moderately in pets. It is not used in agriculture.

Fenbendazole and most other benzimidazoles (e.g. febantel, albendazole, mebendazole, etc.) and tetrahydropyrimidines (e.g. pyrantel, morantel, etc.) have no residual effect, i.e. they act against the worms during a few hours after administration but are quickly metabolized and excreted. For this reason treatment must often be repeated for certain indications. This is in contrast with wormers containing macrocyclic lactones (e.g. milbemycin oxime, selamectin) that ensure protection against numerous roundworms during weeks after a single treatment.

For an overview and a list of the most popular pet wormers click here.


This article IS NOT A PRODUCT LABEL. It offers complementary information that may be useful to veterinary professionals and users that are not familiar with veterinary antiparasitics. 

Information offered in this article has been extracted from publications issued by manufacturers, government agencies (e.g. EMEA, FDA, USDA, etc.) or in the scientific literature. No guarantee is given on its accuracy, integrity, sufficiency, actuality and opportunity, and any liability is denied. Read the site's DISCLAIMER.

In case of doubt contact the manufacturer or a veterinary professional.