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==Introduction==
This group of drugs are derived from ''Streptomyces'' species and are coded as '''3-AV''' products. They are commonly known as '''avermectins''' and '''milbemycins'''. Drugs in use include; '''ivermectin, abamectin, doramectin, moxidectin, eprinomectin''' and '''selamectin'''.
This group of drugs are derived from ''Streptomyces'' species and are coded as '''3-AV''' products. They are commonly known as '''avermectins''' and '''milbemycins'''. Drugs in use include; '''ivermectin, abamectin, doramectin, moxidectin, eprinomectin''' and '''selamectin'''.
==Activity==
==Activity==
* They are inactive against trematodes, cestodes and adult filarial worms. Though are active against migrating heart worm larvae and are used as heartworm prophylactics in cats and dogs.
* They are inactive against trematodes, cestodes and adult filarial worms. Though are active against migrating heart worm larvae and are used as heartworm prophylactics in cats and dogs.
* Their mode of action is by opening invertebrate specific glutamate-gated chloride channels on the post-synaptic membranes. This results in '''flaccid paralysis''' of the parasite.
* Their mode of action is by opening invertebrate specific glutamate-gated chloride channels on the post-synaptic membranes. This results in '''flaccid paralysis''' of the parasite.
==Pharmacokinetics==
==Pharmacokinetics==
* These drugs are excreted very slowly and so the plasma concentration curve has a very long tail.
* These drugs are excreted very slowly and so the plasma concentration curve has a very long tail.
* The initial peak will kill all adult worms and the residual "tail" is able to have a high enough concentration to ensure that infective larvae ingested, for a time after treatment, are incapable of establishing. This provides a '''period of protection against reinfection'''.
* The initial peak will kill all adult worms and the residual "tail" is able to have a high enough concentration to ensure that infective larvae ingested, for a time after treatment, are incapable of establishing. This provides a '''period of protection against reinfection'''.
==Safety==
==Safety==
* These are on the whole safe drugs to use.
* But '''Collie type breeds''' of dogs, especially '''Rough Coated Collies''' can be fatal. This is because they can lack a efflux transporter protein that removes these drugs from the CNS. This means toxic concentrations are capable of accumulating.
* This can also occur when Ivermectin is used at the higher doses needed for some heartworm therapies.
* They are often in high concentrations in faeces, this means that bettles and other insects that use dung-pats for their development can be killed. This is currently a heated topic, especially in areas of a delicate ecosystem.