Macrocyclic lactones (ML)

What do they treat?

 Roundworm  Flies  Ticks  Lice  Mites

Warning: When using MLs to target a particular parasite, be aware that they will also treat any other of the parasites mentioned above that are present. You can increase the development of chemical resistance to all of these parasites each time you use an ML product, including non-target parasites.

Note:  Can kill dung beetles

How can they be administered?

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

 Oral  Pour-on Injection

  • Pour-on formulations exhibit greater variability in absorption than oral or injection.
  • Effective levels are reached in the gastro-intestinal system, lungs, and skin regardless of the route of administration.
  • Note when applied via oral or injection, MLs are not effective against biting lice.


Reported in:  Worms  Ticks (found overseas, so far not in Australia)

Resistance to MLs in Australia is fairly widespread for the small intestinal worm (Cooperia species) and ML resistant populations of small brown stomach worm (Ostertagia ostertagi) have also been found.

What is resistance?


  • Follow the label directions for minimal weight requirements and take care treating underweight animals.
  • Generally, MLs 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 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 macrocyclic lactone

A guide to the different active ingredients and the parasites 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. Macrocyclic lactones, 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.


Pests targeted (may vary with formulation)



Cattle tick




Intestinal tapeworm

Liver fluke

Buffalo fly

Stable fly



























Combination (all actives target boxed parasite)









Abamectin and levamisole





Ivermectin and fluazuron




Moxidectin and levamisole








Abamectin, levamisole and oxfendazole







Mixtures (multiple targets)









Macrocyclic lactone and triclabendazole




Ivermectin and clorsulon




Mixtures and combinations (multiple targets, primary target of actives boxed)









Ivermectin, nitroxynil and clorsulon




What are they?

Macrocyclic lactones are products or chemical derivatives of soil microorganisms belonging to the genus Streptomyces.

How do they work?

MLs have a potent, broad antiparasitic spectrum at low dose levels.

MLs are fast-acting compounds that block nerve transmission in many parasites but have little effect in mammals. They bind to glutamate-gated chloride channel receptors in nerve cells. The resultant sustained channel opening allows influx of chloride ions and paralysis of the parasite neuromuscular system. This reduces the motor capacity of nematodes and causes paralysis, eventually resulting in de-attachment and expulsion from the animal.

MLs become extensively distributed throughout the body and concentrate particularly in fatty tissue. The route of administration and formulation may affect drug absorption, distribution, metabolism, and excretion.