Ectoparasiticides

WIKIDRUGS ANTIPARASITIC DRUGS

These are chemicals used to treat and control parasites that reside on, or in, the skin and coat of animals. They are a diverse set of products that can be applied in various ways. Some important terms must be discussed first before mentioning how each drug works.

Insecticides kill insects, whilst acaricides kill mites and ticks.

Endectocides are active against both endo and ectoparasites. This are discussed on the antihelmintic pages.

Insect Growth Regulators don't kill adult stages but are able to prevent hatching, larval development or metamorphosis.

Modes of Action

These drugs mainly act on the parasites nervous system and neuromuscular junction. They are selectively toxic by having a greater affinity for the parasite receptor than the animal receptor. They can either by contact posions - arbsorbed through the parasites exoskeleton, or are stomach poisons - they are absorbed through the parasites stomach and so the parasite must bite to be affected. Thus the stomach poisons are usually given systemically to the host animal.

Insecticides

Synthetic Pyrethroids - Cypermethrin, Deltamethrin

• Many products and are in widespread use.
• They increase the permeability of neuronal membranes to sodium ions. This makes the membrane hyperxcitable leading to convulsions and death.
• In high concentrations these products can cause adverse reactions in cats and dogs.
• Piperonyl butoxide is a syngeristic product that is often put in formulations to potentiate the action of the pyrethroids.

Semicarbazones - Metaflumizone

• A new group of insecticides
• They work be blocking sodium ion channels in the axonal membrane of nerves, this prevents the propagation of nerve impulses leading to paralysis of the insect and hence death.

Organophosphates and Carbamates - Diazinon, Dichlorvos

• Their use has been limited of late as they are potentially neurotoxic to animals and man, and can cause environmental damage.
• They are anticholinesterases and so resukt in the build up of acetylcholine in the parasites's synapses, leading to paralysis and death.

Neonicotinoids - Imidacloprid, Nitenpyram

• These are mainly used for pest control in crop protection schemes. The above two drugs though are both currently used for flea control.
• They work by stimulating and then blocking post-synaptic nicotinic acetylcholine receptors which leads to paralysis and death.

Phenylpyrazoles - Fipronil, Pyripole

• These are used for flea control and work by blocking GABA transmitted impulses, thus blocking the influx of chlorine ione into nerve cells.

Macrocyclic Lactones - avermectins and milbemycins

• These are endectocides are will be discussed in full on the anti-helminth pages.

Amidines - Amitraz

• This has limited action in veterinary medicine.
• It works by acting on octoparamine receptor sites, these are within parasite muscles, resulting in increased nervous activity, spasming and death.

Inert Inorganics

These are inert substances, often powder, that are used to treat the environment in a properly managed flea control scheme. They work by dessication of the flea eggs or by clogging their spiracles. An example is Sodium polyborate.

Insect Growth Regulators

Insect juvenile hormone analogues - methoprene, pyriproxyfen These work by blocking receptor sites for insect juvenile hormone. This stops the juvenile insect from continuing along it's natural form of devlopment and never reaching adult status.

Chitin Inhibitors - Cyromazine, dicyclanil, lufenuron These likewise block insect development by preventing the insect access to chitin, one of the key components to an adult insect's exoskeleton.