Avermectines (incl. Milbemycines such as Moxidectin) with no antibacterial effect have a macrocyclic lacton in their molecular structure as their common feature. They bind to glutamate-activated chloride channels, typical for invertebrates such as nematodes and arthropods. This increases the membrane permeability in muscle and nerve cells, inhibiting their activity and killing off the parasites. Avermectines are metabolic products from Actinomycetales (Streptomyces) that are subsequently partly chemically modified. Abamectin, one representative of the Avermectines group, is used as a pesticide as a result of its insecticide and acaricide effects.
Benzimidazoles are anthelmintics (drugs used treat parasitic worm infections), which work by binding to specific proteins of the parasitic cells, so-called tubulins. This interrupts the formation of microtubuli, affecting important structural (cytoskeleton) and functional (intake and intracellular transport of nutrients) cell processes, which leads to the killing of the worms and the defecating of them a few days later. The common feature in this substance category is a Benzimidole core in the substances’ molecular structure.
Levamisole is the L-isomer of Tetramisole, which contains the L and R forms in equal parts. Only the L-isomer has an anthelmintic effect, affecting the cholinergic stimuli, resulting in the paralysing and subsequently killing of the parasite.