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MODULE 4 - Infectious Agents > PHARMACOLOGY - Anthelmintics > Flashcards

PHARMACOLOGY - Anthelmintics Flashcards

1
Q

What are the five main classes of anthelmintic drugs used in veterinary medicine?

A
  • Benzimidazoles
  • Levamisoles
  • Macrocyclic lactones
  • Amino-acetonitrile derivatives
  • Multi-actives
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2
Q

What is the spectrum of activity for Benzimidazoles?

A

Effective against all helminths (nematodes, cestodes, tapeworms) including the adult, larvae and egg stages

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3
Q

What is the mechanism of action for Benzimidazoles?

A

Benzimidazoles bind to helminth tubulin preventing microtubule formation and thus starving the parasite

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4
Q

Describe the nature of selective toxicity of Benzimidazoles

A

Benzimidazoles have a higher affinity for helminth tubulin than for mammalian tubulin and bind irreversibly to the helminth tubulin

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5
Q

Why should Benzimidazoles not be used for pregnant patients?

A

Benzimidazoles have been proven to be teratogenic meaning they can cause congenital disease in developing embryos

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6
Q

What is the spectrum of activity for Levamisoles?

A

Effective against adult nematodes

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7
Q

What is the mechanism of action for Levamisoles?

A

Levamisoles act as a nicotinic agonist, stimulating the ganglia of nicotinic acetylcholine receptors leading to sustained muscle contraction and paralysis of the nematode. The nematode can no longer attach to the gut wall and is eventually excreted in the faeces

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8
Q

Describe the nature of toxicity of Levamisoles

A

Levamisoles have a higher affinity for nematode nicotinic acetylcholine receptors than for mammalian nicotinic acetylcholine receptors

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9
Q

(T/F) Levamisoles have a large therapeutic index

A

FALSE. Levamisoles have a narrow therapeutic index

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10
Q

What is important to keep in mind when administering Levamisoles to small animal patients?

A

Small animals are more tolerant to oral administration of Levamisoles than of parenteral administration

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11
Q

Tetrahydropyramidines are derivatives of which drug class?

A

Tetrahydropyramidines are Levamisole derivatives

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12
Q

How do tetrahydropyramidines differ from Levamisoles?

A

Tetrahydropyramidines differ in their pharmacokinetics. These drugs are not well-absorbed from the gastrointestinal tract and are very quickly metabolised

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13
Q

What is the spectrum of activity for Macrocyclic lactones?

A

Macrocylic lactones are endectocides meaning they are effective against nematodes and ectoparasites

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14
Q

What is the mechanism of action for Macrocyclic lactones?

A

Macrocyclic lactones stimulate glutamate-gated chloride channels in invertebrate nerve and muscle cells resulting in flaccid paralysis of the nematode

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15
Q

Describe the nature of selective toxicity of Macrocyclic lactones

A

Macrocyclic lactones target glutamate-gated chloride channels which only exist in nematodes and ectoparasites

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16
Q

Give a specific example of an amino-acetonitrile derivative

A

Monepantel

17
Q

What is the spectrum of activity for Monepantel?

A

Effective against adult nematodes

18
Q

What is the mechanism of action for Monepantel?

A

Monepantel targets a nematode specific subunit of the nicotinic acetylcholine receptor, triggering flaccid paralysis

19
Q

Give a specific example of a Multi-active anthelmintic

A

Derquantel

20
Q

What is the spectrum of activity for Derquantel?

A

Sheep adult nematodes

21
Q

Why should Derquantel only be used for sheep nematodes?

A

Because Derquantel has had adverse effects on small animals and horses

22
Q

What is the mechanism of action for Derquantel?

A

Derquantel acts as a nicotinic antagonist, inhibiting the actions of the nicotinic acetylcholine receptors leading to flaccid paralysis of the nematode

23
Q

Which drug can be used in combination with Derquantel to have an effect against both nematodes, cestodes and trematodes?

A

Praziquantel

24
Q

What is the spectrum of activity for Praziquantel?

A

Effective against adult cestodes and trematodes, unreliable against larval stages

25
Q

What is the mechanism of action for Praziquantel?

A

Praziquantel causes the rapid release of Ca2+ ions from intracellular stores causing tetanic contraction of the helminth musculature leading to paralysis

26
Q

What is the spectrum of activity for Salicylanides and Nitroxynil?

A

Effective against adult trematodes

27
Q

What is the mechanism of action for Salicylanides and Nitroxynil?

A

Salicylanides and Nitroxynil form a proton ionophore in the cell membranes of the trematodes, causing an influx of H+ ions leading to the uncoupling of oxidative phosphorylation. This prevents the trematode from producing energy, eventually killing the trematode

28
Q

Why are Salicylanides and Nitroxynil only effective against adult trematodes?

A

Because these drugs are highly plasma protein bound so can only affect the parasites that are feeding on the blood, i.e. the adult trematodes

29
Q

Why do Salicylanides and Nitroxynil doses need to be repeated at a three week interval?

A

These drugs only target adult trematodes so repeated dosing of these drugs is required at a three week interval to kill any immature trematodes not killed by the previous dose

30
Q

Give an example of a salicylanide anthelmintic

A

Clorsulon

31
Q

What is the spectrum of activity for Clorsulon?

A

Effective against adult Fasciola hepatica (F. hepatica)

32
Q

(T/F) Clorsulon is highly plasma protein bound

A

TRUE

33
Q

Give a specific example of a Cyclooctadepsipeptide drug

A

Emodepside

34
Q

What is the spectrum of activity for Emodepside?

A

Effective against adult nematodes

35
Q

What is the mechanism of action for Emodepside?

A

Emodepside acts as a nicotinic antagonist, inhibiting the actions of the nicotinic acetylcholine receptors leading to flaccid paralysis of the nematode

MODULE 4 - Infectious Agents (20 decks)

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