Benzimidazoles (BZ or ‘white’)

What do they treat?

Roundworm  Tapeworm  Liver fluke

How can they be administered?

A variety of application methods for administering pesticide products to cattle are in use.

Oral

• Always check label information as dose rates for cattle are often higher than those for sheep.

Resistance

Reported in: Roundworm Liver fluke

Resistance to BZs in Australia is fairly widespread for the small brown stomach worm (Ostertagia). It has also been reported in the stomach hair worm (Trichostrongylus axei).

What is resistance?

Safety

• Generally BZs have a wide margin of safety to mammals.

Everyone working in the rural industry has a ‘duty of care’; a legal obligation to provide a safe workplace for everyone on the property.

Withholding

Withholding periods are mandatory with all registered veterinary products used to treat animals for internal and external parasites.

• Always check the product label before use for specific withholding periods (WHP) and export slaughter interval (ESI) periods. Current ESI periods can be confirmed on the APVMA website.

Types of benzimidazoles

A guide to the different actives and the pests they affect are in Table 1. See the Products Search Guides for WormBoss, TickBoss, LiceBoss and FlyBoss for the appropriate formulation and application method for your target pest. Note combinations and mixtures of actives may improve treatment efficacy.

Table 1. Benzimidazoles, their actives, combinations and mixtures and a summary of the targeted parasites for which formulations are registered for. Boxed check marks indicate the pest targeted by multiple actives.

What are they?

Benzimidazoles (BZs) are a large chemical family and the first class of modern anthelmintic developed.

How do they work?

The mode of action of BZs is to bind to a specific building block called beta tubulin in the parasite and so prevent tubulin incorporation into certain cellular structures called microtubules, which are essential for energy metabolism. BZs also have ovicidal activity, which means that they kill worm eggs as they are shed into the gut and excreted.