Anthelmintics Flashcards
Define Anthelmintic
A chemotherapeutic agent used to control helminth infections
Define Chemotherapy
Use drugs to injure an invading organism without injury to the host - selective toxicity dependent
Anthelmintic action can have a ____ or a ____ spectrum
broad or narrow
What is the proper name for white drench? Give a specific example
Benzimidazoles - fenbendazole
What is the proper name for yellow drench? Give a specific example
Imidazothiazoles - levamisole
What is the proper name for clear drench? Give a specific example
Macrocyclic lactones - ivermectin
How do Benzimidazoles act on a helminth?
Block microtubule polymerisation causing inhibition of glucose intake = death
Give an example of a benzimidazoles Anthelmintic used against liver fluke
Triclabendazole
What is potency of Benzimidazoles determined by?
Duration of drug exposure
Will benzimidazoles be more potent in a dog or a ruminant? Why?
Ruminant - slower rate of passage of ingesta so longer exposure
How do Imidazothiazoles act on a helminth? How?
They cause spastic paralysis - accelerate neurotransmission
Give an example of an Imidazothiazole
Levamisole
How do Macrocyclic Lactones act on helminths? How?
They cause flaccid paralysis - blocking neurotransmission
What two types of Macrocyclic Lactones are there?
Avermectins and Milbemycins
Define Metaphylaxis treatment
Treatment of an animal whilst they are being exposed to the helminth
Define Prophylaxis treatment
Treatment of animal before they are let out to pasture to stop the pasture getting contaminated
Describe the action of Praziquantal
Destroys tegument by increasing Ca2+ permeability - causing muscular spasm and release from gut wall
How do Flukicides act on flukes?
The uncouple oxidative phosphorylation decreasing phosphate compound availability - starving parasite
What are the three methods for anthelminthic delivery?
Oral, Parenterally (injection), Topical (trans-dermal)
Give examples of treatment failures
Under dosing Underestimation of bodyweight Inadequate equipment Poor technique Use of incorrect drug Reintroduction into heavily infested pastures Anthelminitc resistance
What is anthelmintic resistance?
ability of worm to tolerate a normally lethal dose
How does anthelmintic resistance occur?
Resistance alleles are already present and spread slowly at first then rapidly as frequency increases
When does anthelmintic resistance become detectable?
When allele frequency is >25%
When does clinical failure of anthelmintics occur?
Normally after allele frequency has breeched 50%
What tests can measure anthelmintic resisitance?
Drench tests and faecal egg count reduction tests
