Anthelmintics Flashcards
Define anthemintic
Chemotherapeutic agent to control helminth infections
Define chemotherapy
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
Nematodicide (roundworms)
Cestodicide (tapeworms)
Trematodicide/flukicide (trematodes/flukes)
How can anthelmintics be delivered? 3
Orally (drench, tablet, oral bolus)
Parentally (injection)
Topically (pour-on)
Overall classifications of anthelmintics -4
- spectrum of activity
- chemical group/mode of action
- target parasites
- method of delivery/formulation
Another name for group 1 benzimidazoles
White drenches
Another name for group 2 LM/imidazothiazoles
Yellow drenches
Another name for group 3 ML
Clear drenches
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?
- ) multiple low doses more potent than one single dose
- ) potency greater in ruminant/horse than dog (rumen/caecum acts as a reservoir)
- ) potency greater in ruminants if starved 12-24hr (slows rate of passage of ingesta)
Another name for Imidazothiazoles/yellow drenches
Tetrahydropyrimidines
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.
Define metaphylaxis
Protection of animals grazing contaminated pasture
Define prophylaxis
preventing pasture infection (i.e. prevents autoinfection peak)
Name the roundwormers - 9
BROAD SPECTRUM:
- Benzimidazoles
- ML
- Imidazothiazoles/tetrahydropyrimidines
- Aminoacetile derivatives (new)
- spiroindoles (new)
NARROW SPECTRUM:
- desipeptides
- salicylanilides
- piperazines
- phenylisothiocyanates
What are monepantel and derquantel?
Examples of new broad spectrum anthelmintics
Name the roundwormers
BROAD SPECTRUM:
- benzimidazoles
- Tetrahydropyrimidines
NARROW SPECTRUM:
- isoquinolines
- phenylisothiocyanates
How does praziquantel (PZQ) work?
Tegument destruction (especially at the proliferation zone) –> increased membrane permeability for calcium ions, loss of intracellular calcium –> spastic paralysis and malabsorption. Ultimately the tapeworm is digested.
Flukicide - spectrum of action
Narrow spectrum target fluke and blood feeding nematodes. Some activity against blood sucking nematodes.
How do flukicides (salicylanilides and substituted phenols) work?
uncouple oxidative phosphorylation decreasing the availability of high energy phosphate compounds
Phamacokinetics - salicylanilides
Binds to plasma proteins –> prolonged plasma half life, not used in milking cattle or sheep.
What is the flukicide of choice for treating acute fasciolosis?
Triclabendazole (for treating flukes down to 2d old)
Define RDR
Recommended Daily Dose
What is fenbendazole (FBZ) active against?
(LS and SS) mucosal larvae
Define excipient
Other ingredients (as opposed to the acitve compound) that alter physical attributes and/or biological properties (e.g help transport drug through skin and into circulation)
3 main ways althelmintics can be delivered
By mouth (oral) - drench, paste, tablet, in feed, bolus
PN (injection) s/c, i/m
Topical (trans-dermal) - pour on
