Avermectin

As avermectins, a group of neurotoxins called that arise as end products of the fermentation of the " rays fungus " Streptomyces avermitilis. In some cases, the fermentation products can be subsequently chemically treated; thereby arise so-called semi-synthetic avermectin.

Chemistry and representatives

Chemically speaking, the avermectins macrolides, i.e., macrocyclic lactones, which include ivermectin, selamectin, doramectin and abamectin.

The derivatives of avermectin are described:

Application and mode of action

Avermectins are used in the control of parasites of domestic animals and livestock as well as prophylactically in crop plants against mites. They show a broad activity against nematodes and mites. Meaningful doses in animals move in the range of 300 micrograms per kg body weight or less; for plant application, a 2 % aqueous emulsion is used. Unlike most other macrolides avermectins show antibacterial or fungicidal activity.

The avermectin neurotoxins increase in invertebrates, the membrane permeability of the nerve or muscle cells for chloride ions by binding to glutamate -activated chloride channels. This leads to hyperpolarization of the cell membrane and to a blocking of the excitation conduction and thus paralysis of the parasites. In addition avermectins affect at higher doses also the receptors for γ -aminobutyric acid ( GABA) in synapses that use GABA as a neurotransmitter. Due to increased release of GABA affected pests are paralyzed and die.

Since GABA is also found in the brains of vertebrates, these drugs can cause side effects and toxic effects that are manifested in fatigue. Especially birds ( especially finches and parakeets here ), rats and animals with MDR1 are relatively sensitive to avermectins. However, in most mammals avermectins not penetrate the blood- brain barrier, whereby they are protected.