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Pharmacology > Anthelmintics > Flashcards

Anthelmintics Flashcards

1
Q

Define anthelmintics and chemotherapy

A

Anthelmintic

  • Chemotherapeutic agent
  • Used to control helminth infections

Chemotherapy

  • Use of drugs to injure an invading organism
  • Without injury to the host
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2
Q

What are the two classes of anthelmintic based on spectrum of activity?

A

Broad - wide range of activity

Narrow - specific target

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3
Q

What are the three classes of anthelmintics based on chemical group/mode of action?

A

Benzimidazoles (fenbendazole)

Imidazothiazoles (levamisole)

Macrocyclic Lactones (ivermectin)

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4
Q

What are the three classes of anthelmintics based on target parasites?

A

Nematocide

Cestodicide

Trematodicide

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5
Q

What are the three classes of anthelmintic based on method of delivery/formulation?

A

Oral

Prenteral

Topical

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6
Q

What are the three main groups of anthelmintics that are broad spectrum?

A

Benzimidazoles (white drenches)

Imidazothiazoles (yellow drenches)

Macrocyclic lactones (clear drenches)

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7
Q

How does each of the five groups of broad spectrum anthelmintics work?

A

Group 1

  • Benzimidazoles
  • Beta-tubulin binding

Group 2

  • Imidazothiazoles
  • ACh agonist

Group 3

  • Macrocyclic lactones
  • Modulate glutamate-gated chloride channels

Group 4

  • Amino-acetonitrile derivatives
  • Targets specific Hco-MPTL receptors

Group 5

  • Spiroindole
  • Ach antagonist
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8
Q

How do benzimidazoles work as anthelmintics?

A

Bind to parasite tubulin

Lead to:

  • Inhibition of glucose uptake
  • Glycogen depletion
  • Death
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9
Q

What determines the potency of benzimidazoles?

A

Duration of exposure

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10
Q

In which animals do benzimidazoles have a greater potency?

A

Ruminant and horse

Rumen/caecum acts as reservoir

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11
Q

How can the potency be increased in ruminants?

A

Starve them for 12-24 hours

Slows rate of passage of ingesta

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12
Q

What do imidazothiazoles/tetrahydropyrimidines cause in parasites?

A

Rapid and reversible spastic paralysis

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13
Q

What are imidazothiazoles now only available as?

A

Oral drenches

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14
Q

Which parasites does levamisole target?

A

Gutworms

Lungworms

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15
Q

How is the half-life of levamisole varied?

A

Route of administration

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16
Q

How long is the half-life of levamisole in the body?

A

Very short

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17
Q

How do macrocyclic lactones work?

A

Open invertebrate spcific glutamate-chloride channels in post-synaptic membrane

Leads to flaccid paralysis

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18
Q

How can you tell a drug is a macrocyclic lactone?

A

Drug usually ends in -ectin

19
Q

Which parasites do macrocyclic lactones work on?

A

Gutworms

Lungworms

Arthropods

20
Q

What is the difference between metaphylaxis and prophylaxis?

A

Metaphylaxis protects animals grazing contaminated pasture

Prophylaxis prevents pasture infection

21
Q

What does the persistent effect and activity of macrocyclic lactones allow?

A

Period of protection against reinfection

Desgin of prophylactic worm control strategies

22
Q

What should be used if anthelmintic resistance is suspected?

A

The smaller groups of broad spectrum anthelmintics

  • Aminoacetile derivatives
  • Spiroindoles
23
Q

What can praziquantel be used for?

A

Echinococcus

24
Q

How does praziquantel work?

A

Destroys tegument

Allows increased membrane permeability for calcium ions

Causes spastic paralysis and malabsorption

Disruption of tegument leads to digestion of tapeworm

25
Q

How do flukicides work?

A

Uncouple oxidative phosphorylation

Decreases availability of high energy phosphate compounds

Starves parasites

26
Q

What are the two types of flukicides?

A

Salicylanilides

Substituted phenols

27
Q

What anthelmintics can’t be used in milking cattle or sheep?

A

Salicylanilides

28
Q

What are the five methods of delivery via the oral route?

A

Drench

Paste

Tablet

In feed

Bolus

29
Q

What are the main nematode species causing disease (PGE) in British sheep?

A
  • Teladorsagia circumcincta*
  • Trichostrongylus* spp.
  • Nematodirus battus*
  • Haemonchus contortus*
  • Cooperia* spp.
30
Q

What is the main nematode species causing PGE in cattle?

A

Ostertagia ostertagi

31
Q

What are the most important horse worms?

A

Strongyles - redworms

32
Q

How do treatment failures occur with anthelmintics?

A

Underdosing

  • Underestimation of bodyweight
  • Inadequae maintenance of equipment
  • Poor technique
  • Failure to follow instructions

Incorrect drug used

Re-introduction of animals onto contaminated pasture

Resistance

33
Q

Describe anthelmintic resistance

A

Parasite can tolerate anthelmintic doses which are normally lethal

Ability is heritable

34
Q

How does resistance appear?

A

Resistance alleles pre-exist in most worm populations

When anthelmintic used very few worms with resistance favoured

Develops slowly at first then more rapidly as allele frequency increases

35
Q

Describe anthelmintic resistance in sheep nematodes

A

Multiple resistance now widely reported

Benzimidazole resistance now widespread

Reports of multiple resistant Teladorsagia circumcincta

36
Q

In what are most macrocyclic lactone resistance reports in cattle?

A

Cooperia spp

37
Q

Describe anthelmintic resistance in horses

A

Benzimidazole resistance widespread in small strongyles (cyathostomins)

Uncommon resistance to pyrantel and macrocyclic lactones

38
Q

How can resistance be measured?

A

In vivo

  • Drench test
  • Wormer test
  • Faecal egg count reduction test

In vitro

  • Larval development assays
  • Egg hatch assay
  • Larval migration inhibition test
39
Q

Describe the drench test

A

Give treatment

FEC on 10 faecal samples post treatment

Test for amount of larval eggs present

40
Q

Describe a faecal egg count reduction test

A

Compare FEC before and after treatment with untreated controls

Resistance indicated if treatment does not reduce FEC by more than 95%

41
Q

What are the 8 steps of the SCOPS outline for sheep?

A
  1. Work out control strategy with vet
  2. Use effective quarantine strategies
  3. Test for AR on farm
  4. Administer anthelmintics effectively
  5. Use anthelmintics only when necessary
  6. Select appropriate anthelmintic for the task
  7. Adopt strategies to preserve worms
  8. Reduce dependence on anthelmintics
42
Q

How should cattle in quarantine be treated with anthelmintics?

A

Two products in different groups sequentially

Hold off pasture for 24-48 hours

Turn out on to dirty pasture

43
Q

Which animal should we dose for with anthelmintics?

A

Heaviest in the group

Pharmacology (3 decks)

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