Anthelmintics

Question 1

Define anthemintic

Answer 1

Chemotherapeutic agent to control helminth infections

Question 2

Define chemotherapy

Answer 2

Use of drugs to injure an invading organism without injury to the host (i.e. selective toxicity)

Question 3

2 spectrums of activity

Answer 3

Broad or narrow

Question 4

Chemical groups of anthelmintics - examples 3

Answer 4

Benzimidazoles (BZ) - fenbendazole
Imidaothiazoles (LM) - levamisole
Macrocyclic lactones (ML) - ivermectin

Question 5

Classification of anthelmintics by target parasite

Answer 5

Nematodicide (roundworms)
Cestodicide (tapeworms)
Trematodicide/flukicide (trematodes/flukes)

Question 6

How can anthelmintics be delivered? 3

Answer 6

Orally (drench, tablet, oral bolus)
Parentally (injection)
Topically (pour-on)

Question 7

Overall classifications of anthelmintics -4

Answer 7

• spectrum of activity
• chemical group/mode of action
• target parasites
• method of delivery/formulation

Question 8

Another name for group 1 benzimidazoles

Answer 8

White drenches

Question 9

Another name for group 2 LM/imidazothiazoles

Answer 9

Yellow drenches

Question 10

Another name for group 3 ML

Answer 10

Clear drenches

Question 11

What are the 2 new groups of broad-spectrum anthelmintic

Answer 11

4 = AD = amino acetonitrile derivatives
5 = SI = spiroindoles

Question 12

What are some examples of narrow spectrum anthelmintics

Answer 12

Fluke drenches, tapewormers, heartworms

Question 13

Examples of benzimidazoles

Answer 13

Albendazole, Fenbendazole, Flubendazole, Mebendazole, Oxfendazole, Triclabendazole

Question 14

Mode of action - BZ

Answer 14

Bind to parasite B-tubulin leading to inhibition of glucose uptake, glycogen depletion and death

Question 15

Administration - BZ

Answer 15

Low water solubility - oral products only. Resuspend prior to administration

Question 16

What determines BZ potency?

Answer 16

Duration of exposure (BZs kill worms very quickly)

Question 17

3 ways to increase BZ potency?

Answer 17

1. ) multiple low doses more potent than one single dose
2. ) potency greater in ruminant/horse than dog (rumen/caecum acts as a reservoir)
3. ) potency greater in ruminants if starved 12-24hr (slows rate of passage of ingesta)

Question 18

Another name for Imidazothiazoles/yellow drenches

Answer 18

Tetrahydropyrimidines

Question 19

Examples of Imidazothiazoles and Tetrahydropyrimidines

Answer 19

Imidazothiazoles - levamisole

Tetrahydropyrimidines - pyrantel

Question 20

How do yellow drenches work?

Answer 20

Cholinergic agonists - cause a rapid and reversible spastic paralysis

Question 21

Administration - yellow drenches

Answer 21

Only available as oral drenches.

Question 22

What does levamisole act on?

Answer 22

Nematodes - especially adult gutworms, less so mucosal larvae and hypobiotic larvae. Also lungworms. NOT trematodes, cestodes, arthropods or protozoa.

Question 23

Administration - levamisole? 3 How does this affect its pharmacokinetics?

Answer 23

Injection - rapid and high peak in plasma concentration, shorter duration of action
Oral - middle peak/duration
Pour-on longer half life, lowest plasma concentration

Question 24

Examples of ML calsses - 2

Answer 24

Avermectins and Milbemycins

Question 25

Mechanism of action - ML

Answer 25

Open invertebrate specific glutamate-chloride channels in post-synaptic membrane leading to flaccid paralysis

Question 26

Spectrum of ML

Answer 26

Broad spectrum - targets all nematode gutworm and lungworm stages. Variable effects on arthropods. Not trematodes, cestodes or protozoa.

Question 27

Pharmacokinetics of MLs

Answer 27

Oral/injection (highest peak) or pour-on. Persistent effect provides period of protection against re-infection. Presistent activity used to design prophylactic worm control strategies.

Question 28

Define metaphylaxis

Answer 28

Protection of animals grazing contaminated pasture

Question 29

Define prophylaxis

Answer 29

preventing pasture infection (i.e. prevents autoinfection peak)

Question 30

Name the roundwormers - 9

Answer 30

BROAD SPECTRUM: - Benzimidazoles - ML - Imidazothiazoles/tetrahydropyrimidines - Aminoacetile derivatives (new) - spiroindoles (new) NARROW SPECTRUM: - desipeptides - salicylanilides - piperazines - phenylisothiocyanates

Question 31

What are monepantel and derquantel?

Answer 31

Examples of new broad spectrum anthelmintics

Question 32

Name the roundwormers

Answer 32

BROAD SPECTRUM: - benzimidazoles - Tetrahydropyrimidines NARROW SPECTRUM: - isoquinolines - phenylisothiocyanates

Question 33

How does praziquantel (PZQ) work?

Answer 33

Tegument destruction (especially at the proliferation zone) --> increased membrane permeability for calcium ions, loss of intracellular calcium --> spastic paralysis and malabsorption. Ultimately the tapeworm is digested.

Question 34

Flukicide - spectrum of action

Answer 34

Narrow spectrum target fluke and blood feeding nematodes. Some activity against blood sucking nematodes.

Question 35

How do flukicides (salicylanilides and substituted phenols) work?

Answer 35

uncouple oxidative phosphorylation decreasing the availability of high energy phosphate compounds

Question 36

Phamacokinetics - salicylanilides

Answer 36

Binds to plasma proteins --> prolonged plasma half life, not used in milking cattle or sheep.

Question 37

What is the flukicide of choice for treating acute fasciolosis?

Answer 37

Triclabendazole (for treating flukes down to 2d old)

Question 38

Define RDR

Answer 38

Recommended Daily Dose

Question 39

What is fenbendazole (FBZ) active against?

Answer 39

(LS and SS) mucosal larvae

Question 40

Define excipient

Answer 40

Other ingredients (as opposed to the acitve compound) that alter physical attributes and/or biological properties (e.g help transport drug through skin and into circulation)

Question 41

3 main ways althelmintics can be delivered

Answer 41

By mouth (oral) - drench, paste, tablet, in feed, bolus PN (injection) s/c, i/m Topical (trans-dermal) - pour on