Pharmacology 6: Anthelmintics

Question 1

Which of the following anthelmintics acts on the parasite neuromuscular system?

Ivermectin
Febantel
Albendazole
Fenbendazole

Answer 1

Ivermectin

Question 2

Group of anthelmintics can be used against nematodes, cestodes and trematodes in ruminants?

Answer 2

Benzimidazoles

Question 3

Anthelmintics can be used against cestodes in small animals?

Answer 3

Praziquantel

Question 4

If two drugs have the same mechanism of action, anthelmintics resistance to one of them means there’s resistance to the second one too?

Answer 4

True

Question 5

Resistance to anti parasitic drugs

problem?
ability to control parasites?
resistance?

Answer 5

*It’s an increasing problem

*Significantly reduces ability to control parasites

*If parasites are resistant to a member of a drug group, assume they are resistant to all members of that group

Question 6

Resistance to antiparasitic drugs- in US

Answer 6

Question 7

What is resistance?

Answer 7

Heritable characteristics

there is no longer affect by drugs by dose or concentraion of compound

Question 8

What percentage of the parasite does a drug have to kill to be affective?

Answer 8

90%

Question 9

Know PROPORTION is different than resistance… why?

Answer 9

Question 10

Does drug resistance start fast or gradually?

Answer 10

Gradually

Question 11

Anthelmintic resistance
grazing animals?

Answer 11

Problem WORSE in grazing animals

Contributing factors
* Animals eat where they defecate
* Kept in groups
* Prevalent approach has been to deworm to prevent any possible problem
from developing
* Widespread use of pour-ons in cattle
* The more often the drug is used, the faster the resistance is developed

Question 12

Factors affecting rate of development of resistance?

1-5 which is worst?

Answer 12

1- scenario 2 (6x years)

2-scenario 1 ( it increases resistance)

3- scenario 1 (under-dosing)

4- scenario 2 ( no expired drug)

5- scenario 2 (pour on is less previously)

Question 13

Which drug is better and why?

Answer 13

Drug 2

because it’s over a longer period of time

Question 14

What kind of proportion of recessive alleles, dominant alleles, and heterozygous alleles

Answer 14

only recessive alleles YOU DO NOT WANT

Question 15

What is the definition of REFUGIA?

Answer 15

Pool of parasites NOT exposed to drug

• These are parasites not exposed to the drug when you give it – not the resistant ones
• This has become one of the most important
  principles in parasite control, especially for grazing animals
• Goal is to dilute resistant genes in the parasite
  population: to delay anthelmintic resistance

Question 16

Why do you want to increase use of targeted selective treatment?

Answer 16

It contributes to the increase of REFUGIA

Question 17

______ target selective treatment= _________ Refugia

Answer 17

INCREASE

INCREASE

Question 18

Do you want to expose all parasites in animals to a drug treatment?

Answer 18

NO

Question 19

What are reasons for apparent treatment failures?

Answer 19

Dose too low

Faulty dosing

wrong drug

animals exposed to overwhelming parasite numbers after treatment with massive reinfection

Question 20

How are we testing for resistance?

Answer 20

with intestinal nematodes, you can compare number of eggs in the feces before and after treatment: fecal egg count reduction test (FECRT)

Question 21

Why is Integral Parasite control is critical?

Answer 21

Anthelmintics barely work at all in small ruminants anymore
* Drug combinations (more than one drugs from different groups given simultaneously
by the same route) used increasingly
* Some Haemonchus resistant to all 3 drug groups

Rapidly headed that way for horses and maybe cattle

Design programs to increase REFUGIA, slow the development of resistance

Requires more methods of parasite control than just use of anthelmintic drugs