Ectoparasiticides Flashcards
Describe how Acute toxicity can develop with use of OPs and How it can be treated
Acute toxicity seen with Muscarinic effects - increased secretions, bronchoconstriction, miosis, intestinal motility, bradycardia, niotinic effects - muscle fasciculation, cramps, weakness, Central - restlessness, convulsions, respiratory and cardiac depression, coma. Tolerance to the muscarinic and nicotinic signs develops. Central - restlessness, convulsions, respiratory and cardiac depression. Treatment- reduce absorption, administer atropine, clear airways, give diazepam to reduce muscular activity. Pralidoxime chloride - specific antidote which enhance the hydrolytic regeneration of the enzyme.
Describe the Site & mechanism of action of the Organophosphates
Acetyl cholinesterase - cholinergic synapses. Organophosphates and AChE form a stable complex, with a slow rate of reactivation - ‘ageing’ of the complex due to loss of one of the alkyl groups. They are extremely lipid soluble. Liver enzymes Activate or detoxify OPs.
What is Neurotoxic Esterase
In cells of the nervous system. Different OPs inhibit NTE to different degrees. Inhibition is followed by changes in structure and function of nerves. The activity of NTE is independent and often reciprocal to acetylcholinesterase activity. Physiological role unknown.
Describe Diazinon as a dip and its uses
It Gives prophylaxis for Psoroptes, ticks, lice and keds, blowfly. There is a 35 day meat withdrawal period. There are Precuations - age restrictions, must have a certificate of competence for sheep dips.
What are the Carbamates?
Ectoparasiticides - eg carbaryl, propoxur. They have anti cholinesterase activity.They are more easily reversed than OPs. They have low mammalian toxicity but carbaryl is carciogenic. Flea collars for cats - contain propxur.
What is the mechanism of Action of the Pyrethroids?
Act on nerve membranes. They modify gating kinetics of sodium channels. They cause neuroexcitation then paralysis. They may also have an effect by inhibiting GABA and glutamate gated channels and VO calcium channels. They have a negative temperature coefficient. Cats are very sensitive. They penetrate cuticle of insect by passive diffusion through wax in pore canals at the tegument, intersegmental membranes. They are metabolised by insect MFOs and esterase’s. Insect resistance mechanisms include behavioural, penetration resistance, site insensitivity, metabolic resistance.
What is cypermethrin?
A pyrethroid - mostly for food producing animals. Available in spray/pour on. Gives prophylaxis for sheep, lambs, head fly, lice, blowfly. 8-12 days Meat withdrawal. Only the Dip has efficacy against Psoroptes - but has been suspended. Deltamethrin and permethrin other pyrethroids.
What is advantix?
A permethrin and imidacloprid (fleas) combination. Prevents from sand flies, mosquitos and stable flies for up to 2–4 weeks, ticks for 3-4 weeks and fleas for up to 4 weeks. Applied as a spot on preparation. Do not use in cats.
What is piperonyl butoxide?
Used alone or to synergise pyrethroids. Inhibits Microsomal enzymes.
What is the mechanism of action of the Amidines?
Monoamine oxidase inhibitor, octopamine receptor agonist, alpha2 receptor agonist. Demodectic mange and sarcoptic mange treatment. Treats fleas and ticks in dogs (Promeris Duo)
What is cyromazine?
Disrupts insect growth regulation, prophylaxis for blowfly, ticks, lice (treatment aswell). 3 day meat withdrawal period.
Describe Benzoyl urea derivative as an ectoparasiticide
An insect growth regulator, benzoyl urea derivative which accumulates in fat, fleas ingest it in blood from host, blocks the formation of larval chitin, inhibits development of flea larvae, no viable eggs produced 24 hours after, oral administration with food monthly.
What is Fipronil?
Blocks GABA gated chloride channels, causes rapid killing of invertebrates, adults killed before egg laying, accumulates in the skin, used in dogs and cats for fleas and ticks, safe to use in puppies and kittens <2days.
Describe the mechanism of Imidacloprid
Chloronicotinyl nitroguanide - binds to CNS nicotinic receptors in the insect, causes paralysis and death. Spot on preparation for flea control in the dog and cat - retained in skin. Monthly treatment.
What is Pyripole?
A phenylpyrazole - spot on solution licensed in dogs only. Used for the treatment and prevention of fleas and ticks. Acts as an antagonist at GABA-gated chloride channels - causes uncontrolled nerve activity leading to death of the parasite. Distributed through the skin and hair - also systemic exposure (toxicity associated with metabolites in overdosing)
