Flashcards in Anthelmintics Deck (41)
Chemotherapeutic agent to control helminth infections
Use of drugs to injure an invading organism without injury to the host (i.e. selective toxicity)
2 spectrums of activity
Broad or narrow
Chemical groups of anthelmintics - examples 3
Benzimidazoles (BZ) - fenbendazole
Imidaothiazoles (LM) - levamisole
Macrocyclic lactones (ML) - ivermectin
Classification of anthelmintics by target parasite
How can anthelmintics be delivered? 3
Orally (drench, tablet, oral bolus)
Overall classifications of anthelmintics -4
-spectrum of activity
-chemical group/mode of action
-method of delivery/formulation
Another name for group 1 benzimidazoles
Another name for group 2 LM/imidazothiazoles
Another name for group 3 ML
What are the 2 new groups of broad-spectrum anthelmintic
4 = AD = amino acetonitrile derivatives
5 = SI = spiroindoles
What are some examples of narrow spectrum anthelmintics
Fluke drenches, tapewormers, heartworms
Examples of benzimidazoles
Albendazole, Fenbendazole, Flubendazole, Mebendazole, Oxfendazole, Triclabendazole
Mode of action - BZ
Bind to parasite B-tubulin leading to inhibition of glucose uptake, glycogen depletion and death
Administration - BZ
Low water solubility - oral products only. Resuspend prior to administration
What determines BZ potency?
Duration of exposure (BZs kill worms very quickly)
3 ways to increase BZ potency?
1.) multiple low doses more potent than one single dose
2.) potency greater in ruminant/horse than dog (rumen/caecum acts as a reservoir)
3.) potency greater in ruminants if starved 12-24hr (slows rate of passage of ingesta)
Another name for Imidazothiazoles/yellow drenches
Examples of Imidazothiazoles and Tetrahydropyrimidines
Imidazothiazoles - levamisole
Tetrahydropyrimidines - pyrantel
How do yellow drenches work?
Cholinergic agonists - cause a rapid and reversible spastic paralysis
Administration - yellow drenches
Only available as oral drenches.
What does levamisole act on?
Nematodes - especially adult gutworms, less so mucosal larvae and hypobiotic larvae. Also lungworms. NOT trematodes, cestodes, arthropods or protozoa.
Administration - levamisole? 3 How does this affect its pharmacokinetics?
Injection - rapid and high peak in plasma concentration, shorter duration of action
Oral - middle peak/duration
Pour-on longer half life, lowest plasma concentration
Examples of ML calsses - 2
Avermectins and Milbemycins
Mechanism of action - ML
Open invertebrate specific glutamate-chloride channels in post-synaptic membrane leading to flaccid paralysis
Spectrum of ML
Broad spectrum - targets all nematode gutworm and lungworm stages. Variable effects on arthropods. Not trematodes, cestodes or protozoa.
Pharmacokinetics of MLs
Oral/injection (highest peak) or pour-on.
Persistent effect provides period of protection against re-infection. Presistent activity used to design prophylactic worm control strategies.
Protection of animals grazing contaminated pasture
preventing pasture infection (i.e. prevents autoinfection peak)