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 be treating any other of the above-mentioned parasites that are present. This can increase the development of chemical resistance by all of these parasites each time an ML product is used.

Note: Can kill dung beetles

How can they be administered?

Oral  Pour-on  Injection

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

  • 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)

What is resistance?


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

  • Generally ML’s have a wide margin of safety to mammals.


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 actives and the pests they affect are in Table 1. See the Products Search Guides for LiceBoss, WormBoss, TickBoss 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



Round worm

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)









Ivermectin, nitroxinil 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.