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CVSOH BVSc3 > Anthelmintics > Flashcards

Anthelmintics Flashcards

1
Q

What is an anthelmintic agent?

A

Expel parasitic worms from the body by stunning or killing the parasites

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2
Q

What do helminths require?

A

A feeding site
A working GI tract
Neuromuscular coordination
Homeostasis

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3
Q

What are the different preparations of anthelmintic agents?

A

Oral preparations
Slow release bolus
Pro drug
Injections

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4
Q

What are the 3 mechanisms of action of anthelmintic agents?

A

Affect microtubular function
Cause helminth paralysis
Affect energy-generating systems

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5
Q

What are the 5 classification groups of anthelmintic agents?

A 
Benzimidazoles
Levamisole
Macrocyclic lactone
Amino-acetonitrile derivatives 
Spiroindoles
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6
Q

What are the properties of an ideal anthelmintic?

A 
Selective toxicity - wide therapeutic index
Broad spectrum of activity
Cost effective
Drug resistance not likely
Efficacy and potency
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7
Q

What is benzimidazoles mechanism of action?

A

Compromises beta-tubulin cytoskeleton

Glucose uptake is microtubule dependent - causes starvation

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8
Q

What spectrum of activity are benzimidazoles?

A

Wide

Mostly nematodes

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9
Q

What is a pro-drug?

A

Inactive compound that is metabolised in the body to make it biologically active

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10
Q

What is an example of a pro-drug?

A

Febantel

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11
Q

What factors affect benzimidazoles efficacy?

A

Diet - fibre
GI flow rate
Parasite infection
Ruminant oesophageal groove closure

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12
Q

What neurotransmitters do helminths use?

A

Cholinergic (ACh) - excitation

GABAergic - inhibition

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13
Q

What is levamisole’s mechanism of action?

A

Prolonged activation of excitatory nicotinic ACh receptors - Nicotinic receptor agonists
Spastic muscle paralysis

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14
Q

What are the two groups of levamisoles?

A

Imidazothiazoles and tetrahydropyrimidines

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15
Q

What are the two semisynthetic derivatives of macrocyclic lactones?

A

Avermectins

Milbemycins

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16
Q

What is the mechanism of action of avermectins?

A

Activate the glutamate-gated chloride channels - targets neuromuscular junction
Causes flaccid paralysis/starvation

17
Q

What toxicity can be caused by avermectin?

A

MDR1 gene in collies

18
Q

What is the difference between milbemycin and avermectin?

A

Milbemycin has a longer half life
Also effects ticks and fleas
Given in combination with praziquantel

19
Q

What is the mechanism of action of amino-acetonitrile derivatives?

A

Activate the nematode specific ACh receptor

Causes irreversible paralysis

20
Q

What are amino-acetonitrile derivatives active against?

A

Adults and maturing larvae

Triple resistant nematodes

21
Q

What is the mechanism of action of spiroindoles?

A

Block cholinergic neuromuscular transmission

Flaccid paralysis

22
Q

What are spiroindoles used to treat?

A

Broad range of adult/immature nematodes in sheep

23
Q

What anthelmintic is used to treat tapeworms?

A

Praziquantel

24
Q

What is the mechanism of action of praziquantel?

A

Increases the permeability of cell membranes to Ca2+

Sustained muscle contraction and tegmental disruption

25
Q

What are the main trematodal agents?

A

Triclabendazole - fasciola hepatica

26
Q

What is anthelmintic resistance?

A

The ability of parasites to survive treatments at the reccomended dose rate

27
Q

What is the clinical definition of resistance?

A

95% or less reduction in a faecal egg count test

28
Q

What is triple resistance?

A

Resistance to the 3 different anthelmintic agents
1 - BZ
2 - LV
3 - ML

29
Q

What human factors contribute to resistance?

A

Under dosing
Unnecessary dosing
Misdiagnosis - inappropriate drugs

30
Q

What helminth factors contribute to resistance?

A

Molecular changes
Modified activity of parasitic enzymatic systems
Changes to receptors
Amplification of target genes

31
Q

What causes benzimidazole resistance?

A

Cross resistance due to altered beta-tubulin

32
Q

What causes Levamisole resistance?

A

Modified nicotinic ACh receptors - altered drug binding

33
Q

What causes Macrocyclic lactone resistance?

A

Alterations in multiple genes

34
Q

How to minimise resistance?

A

Cycle through classes
Combination products
Correct dosing and product

35
Q

What is an example of a combination product?

A

Abamectin and derquantel

36
Q

What is an example of a parasite that has a vaccination?

A

Dictyocaulus viviparus

37
Q

What are some alternative options to anthelmintics?

A

Use genetically resistant host species
Nematophagous fungi
Vaccination

CVSOH BVSc3 (60 decks)

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