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Pharmacology > Anthelmintics > Flashcards

Anthelmintics Flashcards

1
Q

What are the 5 main classes of anthelmintics?

A 
Group 1 - Benzimidazoles
Group 2 - Levamisoles
Group 3 - Macrocyclic lactones
Group 4 - Amino acetonitrile derivatives
Group 5 - Multi-actives
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2
Q

Which group is aka ‘white drenches’?

A

Benzimidazoles

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3
Q

Which group is aka ‘yellow drenches’?

A

Levamisoles

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4
Q

Which group is aka ‘clear drenches’?

A

Macrocyclic lactones

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5
Q

Which group is aka ‘orange drenches’?

A

Amino acetonitrile derivatives

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6
Q

Which group is aka ‘purple drenches’?

A

Multi-actives

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7
Q

What is the primary action of benzimidazoles?

A

Bind tubulin to prevent microtubule formation, starves the parasite, killing it.
Acts for 6-24hrs.

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8
Q

What are other actions of benzimidazole?

A
  1. Inhibits mitochondrual fumarate reductase
  2. Reduces glucose transport
  3. Uncoupling of oxidative phosphorylation
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9
Q

What is the spectrum of activity of benzimidazoles?

A

Broad spectrum. Effective against all 3 types of helminth, larvae and eggs.

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10
Q

Are there any side effects to benzimidazoles?

A

Well tolerated, characteristically free of side effects.

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11
Q

Describe the pharmacokinetics of benzimidazoles

A
  • Oral administration
  • Limited absorption from GIT (<1% oral dose in plasma)
  • Efficacy increased if gut transit time decreased
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12
Q

Describe the mechanism of action of the levamisoles

A
  • Ganglion stimulant, nicotinic agonist
  • Paralyses helminth by sustained muscle contraction, loses ability to hold onto site in body, passed in faeces, coughing
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13
Q

Are there any side effects associated with levamisoles?

A
  • Reflect nicotinic stimulation of animal

- Safety margin, 4-12 x therapeutic dose

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14
Q

What is the spectrum of activity of levamisoles?

A

Nematodes.

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15
Q

Describe the pharmacokinetics of the levamisoles

A
  • Highly water soluble and is absorbed and excreted rapidly

- >24hrs, <1% initial dose left in tissues

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16
Q

Describe the mechanism of action of the macrocyclic lactones

A
  • Stimulate glutamate-gated chloride channels in nerve and muscle cells
  • Cl- influx, hyperpolaristation of post-synaptic cell, interfering with neurotransmission
  • Results in flaccid paralysis
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17
Q

What is the spectrum of activity of macrocyclic lactones?

A

Nematodes and ectoparasites

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18
Q

Describe the pharmacokinetics of macrocyclic lactones

A

Given topically, v lipid soluble, long half life

19
Q

Are there any side effects associated with macrocyclic lactones?

A
  • Generally safe and well tolerated

- Exceptions are in mdr 1 deficient animals, drug enters CNS so are susceptible to effects

20
Q

What is the nature of the selective toxicity of macrocyclic lactones?

A

Mammalian glutamate receptors are in CNS. ML lipid soluble so can cross into CNS. P-glycoprotein pump extrudes drug immediately from CNS, stopping drug accumulating and having effect on host.

21
Q

Give an example of a drug in the amino acetonitrile derivative group

A

Monepantel

22
Q

What is the mechanism of action of monepantel?

A

Targets nematode specific subunit of nicotinic ACh receptor

23
Q

Are there any side effects associated with monepantel?

A

None reported

24
Q

What is the spectrum of activity of monepantel?

A

Nematodes

25
Q

Describe the pharmacokinetics of monepantel

A

Readily absorbed and oxidised to a sulfone metabolite which is excreted in urine and bile.

26
Q

Name 4 other anthelmintic classes

A

Praziquantel
Salicylanides
Clorsulon
Cyclooctadepsipeptides

27
Q

Give an example of drug belonging to the multi-actives group

A

Derquantel

28
Q

What is the mechanism of action of derquantel?

A

Nicotinic antagonist

29
Q

What is the spectrum of activity of derquantel?

A

Sheep nematodes

30
Q

Are there any safety issues associated with the use of derquantel?

A
  • 4.5 x therapeutic dose causes dullness, depression, incoordination, weakness, decreased GI motility, abnormal breathing pattern, recumbancy, death
31
Q

Describe the mechanism of action of praziquantel

A
  • Tetanic contraction of parasite musculature
  • Rapid vacuolisation of syncitial tegument
  • Releases intracellular Ca, muscle contraction, water drawn in, parasite ruptures and bursts
32
Q

What is the spectrum of activity of praziquantel?

A

Cestodes and trematodes

33
Q

Describe the pharmacokinetics of praziquantel

A

Widely absorbed and distributed

34
Q

Describe the mechanism of action of the salicyclanides

A
  • Creates proton ionophore

- Influx of H+, decrease pH, uncoupling of oxidative phosphorylation

35
Q

What is the spectrum of activity of the salicyclanides?

A

Trematodes

36
Q

Describe the pharmacokinetics of salicyclanides

A
  • Readily absorbed from GIT

- Highly bound by plasma proteins

37
Q

Are there any risks associated with salicylanides?

A

No direct effect on mammalian cells

38
Q

Describe the mechanism of action of clorsulon

A
  • Inhibits 3-phosphoglycerate kinase and phosphoglyceromutase
  • Blocks glycolytic pathway
39
Q

What is the spectrum of activity of clorsulon?

A

Adult F. hepatica

40
Q

Describe the mechanism of action of the cylclooctadepsipeptides

A
  • Inhibits release of ACh from pre-synaptic neurone

- Flaccid paralysis and death

41
Q

What is the spectrum of activity of the cyclooctadepsipeptides?

A

Adult nematodes

42
Q

What are the 5 routes of administration used for anthelmintics?

A
  1. Drench
  2. Bolus
  3. Pour on
  4. Injectable
  5. Oral
43
Q

What will a good worming strategy include?

A
  • Testing (FEC)
  • Reporting lack of efficacy
  • Grazing management
  • Weighing animals to administer right dose
  • Avoiding unnecessary treatment

Pharmacology (9 decks)

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