Anthelmintics

Question 1

What are the two methods to controlling/treating parasite infections?

Answer 1

• Anthelmintics: using drugs to prevent parasites and transmission
• Non-drug related parasitic control strategies: faecal collection, grazing strategies

Question 2

What are the 2 strategies for anthelmintic use?

Answer 2

• Prophylactic: prevent disease

- Therapeutic: when cases are identified

Question 3

What considerations need to be made when using anthelmintics?

Answer 3

• Spectrum of activity
• Pharmokinetics e.g. withdrawal periods, absorption, excretion
• Formulation and administration
• Drug efficacy
• Drug resistance
• Toxicity and specificity
• Cost

Question 4

What are the 3 ‘old’ classes of anthelmintics?

Answer 4

1BZ = Benzimidazoles
2LEV = Imidathiozoles, tetrahydropyrimidines 
3ML = Macrocyclic lactones

Question 5

What are the 2 ‘new’ classes of anthelmintics?

Answer 5

4-AD = Amino acetonitrile derivatives
5-SI = Spironidoles

Question 6

What is the mode of action of BZs?

Answer 6

• bind to a microtubule subunit protein, beta-tubulin
• inhibit microtubule mediated transport of secretory vesicles
• prevents polymerisation

Question 7

Describe the spectrum of activity of BZs

Answer 7

• Not well absorbed systemically
• Primarily target nematodes in the gut
• Ovicidal = kills parasites and eggs
• Effective at targeting hypobiosed larvae

Question 8

Where do LEVs acton?

Answer 8

• Act on nicotinic acetyl choline receptors (nAChR)
• Somatic muscle cells
• Paralyze the parasite

Question 9

Describe the spectrum of activity of LEVs

Answer 9

• Not well absorbed systemically
• Primarily targets nematodes: Gut dwelling stages
• Short acting

Question 10

Of the 3 ‘old’ drug classes, which is mostly used?

Answer 10

MLs as they are highly effective

Question 11

What is the mode of action of MLs?

Answer 11

• Act on nervous system of parasite: musculature and pharyngeal pumping
• Cause hyperpolarisation: multiple targets including glutamate-gated chloride channels

Question 12

Describe the spectrum of activity of MLs

Answer 12

• Well absorbed systemically
• Effective against nematodes only
• Target multiple nematode stages: Migrating larvae, hypobiotic larvae
• Have residual activity
• Target internal and external parasites = endectocide

Question 13

Why were two new anthelmintic groups made?

Answer 13

As a response to the problems of anthelmintic resistance

Question 14

Describe the spectrum of activity of 4-AD

Answer 14

• 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

Question 15

Describe the spectrum of activity of 5-SI?

Answer 15

• 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

Question 16

Name the anthelmintic used to treat tapeworm

Answer 16

Praziquantel

Question 17

What are combination drugs?

Answer 17

Combining two drugs from different drug classes with different spectrums of activity
- form a single drug treatment