Anthelmintic Drugs

How many major classes of anthelmintics are there?

5

What are the 2 possible strategies to control gastrointestinal nematodes?

non-drug related control - faecal collection from pastures, grazing strategies

anthelmintic treatment

What features of anthelmintic drugs affect their use?

spectrum of activity

dosage

pharmacokinetics

formulation

administration route

efficacy

drug resistance

toxicity

cost

What are the 5 classes of anthelmintic drug?

benzimidazoles

imidathiozoles, tetrahydropyrimidines (lovamasoles)

macrocyclic lactones

amino acetonitril derivatives

spiroindoles

What are the features of benzimidazoles?

successful and potent drugs

can be further modified to give prodrugs

not well absorbed systemically

primarily target nematodes

ovicidal (only drug to do this)

effective at targeting hypobiosed larvae

How do benzimidazoles work?

they bind to the microtubule subunit protein beta-tubulin an prevent the microtubule from being formed properly, which prevents transport of secretory vesicles and enzymes

What are the features of imidathiazoles/ tetrahydropyrimidines?

least well absorbed systemically

primarily targets nematode

short acting

gut dwelling stages

How do imidathiazoles/ tetrahydropyrimidines work?

they act on nicotinic acetly choline receptors on somatic mucle cells which causes paralysis and expulsion

What are the features of macrocyclic lactones?

well absorbed systematically

effective against nematodes only

target multiple nematode stages

residual activity - ensures any remaining are killed off

endectocide - target internal and external parasites

Which 2 drug types are found within macrocyclic lactones?

avermectins and milbemycin oxine

How do macrocyclic lactones work?

stored in fat tissue from which they are slowly released

act on nervous system of the parasite (not sure exactly how)

absorbed well systemically because they are highly lipophilic

potentiators cause hyperpolarisation

What are the features of amino acetonitrile derivatives?

primarily targets nematodes

relatively short acting

targets adults and L4-larvae of the most important species

How do amino acetonitrile derivatives work?

via distinct nicotinic acetyl choline receptors (slightly unknown)

What are the features of spiroindoles?

narrow spectrum

effective against some GI nematodes of sheep

gut dwelling only - ineffective against roundworns outside the digestive tract

short acting

How do spiroindoles work?

a combination of drugs block cholinergic neuromuscular transmission, causing paralysis and expulsion

What is praziquantel?

a potent anti-cestode (taperworm) drug

What are some anthelmintic drugs not included in the 5 main categories?

praziquantel

depsipeptide

flukicides

What are combination anthelmintics?

2 anthelmintic drugs from different drug classes with different spectrums of activity which are combined to create extended activity from the treatment