The milbemycins are a group of macrolides chemically related to the avermectin

Avermectin

The avermectins are a series 16-membered macrocyclic lactone derivatives with potent anthelmintic and insecticidal properties. These naturally occurring compounds are generated as fermentation products by Streptomyces avermitilis, a soil actinomycete...

s and were first isolated in 1972 from Streptomyces

Streptomyces

Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...

 hygroscopicus.
They are used in veterinary medicine as antiparasitic agents against worms, ticks and fleas.

Mechanism of action

Like avermectins, milbemycins are products of fermentation

Fermentation (biochemistry)

Fermentation is the process of extracting energy from the oxidation of organic compounds, such as carbohydrates, using an endogenous electron acceptor, which is usually an organic compound. In contrast, respiration is where electrons are donated to an exogenous electron acceptor, such as oxygen,...

 by Streptomyces

Streptomyces

Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...

species. They have a similar mechanism of action, but a longer half-life than the avermectins. They open glutamate sensitive chloride channel

Chloride channel

Chloride channels are a superfamily of poorly understood ion channels consisting of approximately 13 members.Chloride channels display a variety of important physiological and cellular roles that include regulation of pH, volume homeostasis, organic solute transport, cell migration, cell...

s in neuron

Neuron

A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...

s and myocyte

Myocyte

A myocyte is the type of cell found in muscles. They arise from myoblasts.Each myocyte contains myofibrils, which are long, long chains of sarcomeres, the contractile units of the cell....

s of invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s, leading to hyperpolarisation of these cells and blocking of signal transfer.

Examples

Name	=R1	=R2	–R3
Milbemectin	–H, (β)–OH	–H, –H	–CH3 : –CH2CH3 = 3:7
Milbemycin oxime Milbemycin oxime Milbemycin oxime is a veterinary drug from the group of milbemycins, used as a broad spectrum antiparasitic. It is active against worms , insects and mites ....	=NOH	–H, –H	–CH3 : –CH2CH3 = 3:7
Moxidectin Moxidectin Moxidectin is a parasiticide used for the prevention and control of heartworm and intestinal worms, and can be found in treatments prescribed for animals such as dogs, cats, horses, cattle and sheep. It is also used for the prevention of red mite in caged birds...	–H, (β)–OH	=NOCH3	(Z)–C(CH3)=CH–CH(CH3)2
Nemadectin	–H, (β)–OH	–H, (α)–OH	(Z)–C(CH3)=CH–CH(CH3)2