Anthelmintics

Question 1

What is an anthelmintic?

Answer 1

Chemotherapeutic agent used to control helminth infections

Question 2

What is chemotherapy?

Answer 2

Use of drugs to injure an invading organism without injury to the host => SELECTIVE TOXICITY

Question 3

What are anthelmintics classified by?

Answer 3

1. Spectrum of activity (broad/narrow)
2. Chemical group/mode of action (Benzimidazoles, Imidazothiazoles, Macrocydic lactones)
3. Target parasites (Nemo, cesto, trema)
4. Method of delivery (orally, parenterally, topically)

Question 4

Examples of broad spectrum anthelmintics…

Answer 4

1. Group 1
   Benzimidazoles
   (White drench)
2. Group 2
   Imidazothiazoles
   (Yellow drench)
3. Group 3
   Macrocyclic lactones
   (Clear drench)
4. Group 4
   Amino acetonitrile derivatives
5. Group 5
   Spiroindoles

Question 5

Give examples of narrow spectrum anthelmintics..

Answer 5

Salicylanilides - Flukes
Pyrazinoisoquinolines - Tapeworm
Depsipeptides - COPD
Arsenicals - Heartworm
Piperazines

Question 6

What is the mode of action of benzimidazoles?

Answer 6

Microtubules made up of B-tubulin move nutrients from gut to parasite.
Benzimidazoles prevent microtublin formation = PARASITE STARVES

Question 7

Give examples of benzamidazoles….

Answer 7

Fenbendazole
Albendazole
Flubendazole
Mebendazole
Oxfendazole

Question 8

What is the mode of action in group 2-5 anthelmintics?

Answer 8

Distrust neuromuscular junction

Question 9

Key points about benzimidazoles

1. Colour
2. Water solubility
3. Spectrum of activity
4. Mode of action

Answer 9

1. White drench
2. Low solubility (oral only)
3. Broad spectrum (gut and lung)
4. Bind to parasite tubulin and inhibits glucose uptake

Question 10

Describe the pharmacokinetics of benzimidazoles….

Answer 10

Starves helminths out slowly, so slower acting drug more potent and effective

Question 11

Why is benzimidazole more potent in ruminants/horses than dogs?

Answer 11

Rumen/caecum acts as a reservoir

Question 12

Key points about imidazothiazoles…

1. Colour
2. Spectrum of activity
3. Mode of action

Answer 12

1. Yellow drench
2. Broad spectrum
3. Cholinergic agonists => rapid and reversible SPASTIC PARALYSIS

Question 13

Give examples of

1. Imidazothiazoles
2. Tetrehydropyrimidines

Answer 13

1. Levamisole

2. Pyrantel

Question 14

Examples of macrocyclic lactones…

Answer 14

Milbemycin

Avermectins

Question 15

Key points about macrocyclic lactones:

1. Colour
2. Spectrum of activity
3. Mode of action

Answer 15

1. Clear drench
2. Very broad spectrum (guts, lung and arthropods)
3. Open glutamate chloride channels in post synaptic membrane => FLACCID PARALYSIS

Question 16

What is metaphylaxis?

Answer 16

Animal treated for protection when it is already contaminated pasture

Question 17

What is prophylaxis?

Answer 17

Animal treated before turned out to pasture in an attempt to prevent pasture contamination

Question 18

What is the mode of action of praziquantel?

Answer 18

Disrupts tegument - increase permeability

Inflow of Ca ions - parasite muscle spasms

Spastic paralysis - release hold on gut wall

Digestion of tapeworm

Question 19

Key points about flukicides

1. Spectrum of activity
2. Mode of action

Answer 19

1. Narrow spectrum - target fluke and blood feeding nematodes
2. Uncouples oxidative phosphorylation - parasite starves

Question 20

Examples of fluckicides…

Answer 20

Salicylanilides
Sunstituted phenols
Benzimidazoles

Question 21

Pharmacokinetics of salicylanilides

Answer 21

Binds to plasma proteins - prolonged half life (not used in milk cattle/sheep)

Some activity against blood sucking nematodes e.g. haemonchus