What are the two methods to controlling/treating parasite infections?
- Anthelmintics: using drugs to prevent parasites and transmission
- Non-drug related parasitic control strategies: faecal collection, grazing strategies
What are the 2 strategies for anthelmintic use?
- Prophylactic: prevent disease
- Therapeutic: when cases are identified
What considerations need to be made when using anthelmintics?
- Spectrum of activity
- Pharmokinetics e.g. withdrawal periods, absorption, excretion
- Formulation and administration
- Drug efficacy
- Drug resistance
- Toxicity and specificity
- Cost
What are the 3 ‘old’ classes of anthelmintics?
1BZ = Benzimidazoles 2LEV = Imidathiozoles, tetrahydropyrimidines 3ML = Macrocyclic lactones
What are the 2 ‘new’ classes of anthelmintics?
4-AD = Amino acetonitrile derivatives 5-SI = Spironidoles
What is the mode of action of BZs?
- bind to a microtubule subunit protein, beta-tubulin
- inhibit microtubule mediated transport of secretory vesicles
- prevents polymerisation
Describe the spectrum of activity of BZs
- Not well absorbed systemically
- Primarily target nematodes in the gut
- Ovicidal = kills parasites and eggs
- Effective at targeting hypobiosed larvae
Where do LEVs acton?
- Act on nicotinic acetyl choline receptors (nAChR)
- Somatic muscle cells
- Paralyze the parasite
Describe the spectrum of activity of LEVs
- Not well absorbed systemically
- Primarily targets nematodes: Gut dwelling stages
- Short acting
Of the 3 ‘old’ drug classes, which is mostly used?
MLs as they are highly effective
What is the mode of action of MLs?
- Act on nervous system of parasite: musculature and pharyngeal pumping
- Cause hyperpolarisation: multiple targets including glutamate-gated chloride channels
Describe the spectrum of activity of MLs
- Well absorbed systemically
- Effective against nematodes only
- Target multiple nematode stages: Migrating larvae, hypobiotic larvae
- Have residual activity
- Target internal and external parasites = endectocide
Why were two new anthelmintic groups made?
As a response to the problems of anthelmintic resistance
Describe the spectrum of activity of 4-AD
- Targets adults and L4 larvae
- Primarily targets nematodes
- Shown to be effective against parasite species resistant to actives 1-BZ, 2-LEV, 3-ML
- Relatively short acting – no residual activity
Describe the spectrum of activity of 5-SI?
- Narrow-spectrum anthelmintic effective against some GI nematodes of sheep.
- Gut dwelling stages only - it is ineffective against roundworms outside the digestive tract
- Shown to be effective against parasite species resistant to actives 1-BZ, 2-LEV, 3-ML
- Short acting
Name the anthelmintic used to treat tapeworm
Praziquantel
What are combination drugs?
Combining two drugs from different drug classes with different spectrums of activity
- form a single drug treatment
