Parasitology slide set 2

Question 1

Trends in development of vet parasiticides

Answer 1

Broad spectrum

ease of application

Question 2

antiparasitic drugs

Answer 2

called anthelmintics

most widely used are the “modern anthelmintics”

Question 3

“Modern” anthelmintics

Answer 3

developed sine 1960
broad spectrum
high safety margin

Question 4

Members of the benzimidazoles and probenzimidazoles

Answer 4

fenbendazole (horse, cow, goat, pig, dog)
albendazole (sheep, cow, goat)
oxibendazole (horse)
oxfendazole (horse, cow)
febantel (dog, once metabolized becomes fenbendazole)

Question 5

Mode of action of benzimidazoles and probenzimidazoles

Answer 5

affects tubulin and microtubule assembly
Needs to stay around for awhile to work, usually better to give more often than to increase dose
Fenbendazole needs to be given with food for small animals

Question 6

Members of tetrahydropyrimidines

Answer 6

pyrantel

morantel

Question 7

Mode of action of tetrahydropyrimidines

Answer 7

acetylcholine agonist

Question 8

Member of imidazothiazoles

Answer 8

levomisole

Question 9

Mode of action of imidazothiazoles

Answer 9

acetylcholine agonist

Question 10

Members of avermectins/milbemycins (aka macrolides or macrocyclic lactones)

Answer 10

Avermectins: ivermectin
doramectin
eprinomectin
selamectin
Milbemycins: moxidectin
milbemycin

Question 11

Mode of action of avermectins/milbemycins (aka macrolides or macrocyclic lactones)

Answer 11

affects glutamate gated chloride channels leading to hyperpolarization of nerves and muscles, also affect reproduction
Often have residual activity b/c are more lipohilic (milbemycins more so than avermectins)

Question 12

Members of isoquinolines

Answer 12

praziquantel

epsiprantel

Question 13

Mode of action of isoquinolines

Answer 13

affects cell membrane permeability; tetanic contraction of muscles probably related to changes in permeability of tegument to calcium

Question 14

Side resistance

Answer 14

if resistant to one member of a group, resistant to all members of the group
Important in benzimidazoles and macrolides

Question 15

Cross resistance

Answer 15

occurs when resistance to one group confers resistance to another group; don’t see this much
Imidithiazoles and tetrahydropyrimidines

Question 16

Spectrum of action of benzimidazoles

Answer 16

Nematodes- adult, most are larvividal (but may need to increase dose)
Tapeworms and flukes- albendazole and fenbendazole have some activity

Question 17

Administration of benzimidazoles and probenzimidazoles

Answer 17

oral only, poorly water soluble

Question 18

Withdrawal times for benzimidazoles and probenzimidazoles

Answer 18

Meat withdrawal days to weeks

Milk withdrawal- none with fenbendazole, others are not approved for lactation or have withdrawal

Question 19

Safety in benzimidazoles

Answer 19

Usually very safe

Exceptions: albendazole- ruminants in early pregnancy; febntel- dogs during pregnancy

Question 20

Benzimidazole resistance in US

Answer 20

Cases described in: strongylid nematode parasites in horses, small ruminants, and cattle
Also for equine ascarids (roundworms)

Question 21

There is cross resistance between imidazothiazoles and

Answer 21

tetrahydropyrimidines; specifically levamisole, pyrantel, morantel

Question 22

Mode of action of levamisole, pyrantel, morantel

Answer 22

Cholinergic agonists- depolarizing neromuscular blocking agets
Rapid, reversible spastic paralysis of worms, eliminated by normal gut activity

Question 23

Administration of levamisole, pyrantel, morantel

Answer 23

primarily oral

Question 24

Withdrawal time of levamisole, pyrantel, morantel

Answer 24

Meat- days

Morantel- no milk withdrawal, others not approved for lactating food animals

Question 25

Spectrum of action of levamisole, pyrantel, morantel

Answer 25

Adult nematodes

Pyrantel used for horse tapeworms in the past

Question 26

Safety of levamisole, pyrantel, morantel

Answer 26

Good, levmisole associated with most problems- might see salivation, tremors usually in small ruminants

Question 27

Resistance described for levamisole and pyrantel

Answer 27

Levamisole- small ruminant strongylids
Pyrantel- horse strongylids, ascarids
Generally assume cross resistance of imidithiazoles and tetrahydropyrimidines

Question 28

Macrocyclic lactones (macrolides) general info

Answer 28

Called endectocides b/c have activity against internal and external parasites
Originally fermentation products of soil microbes

Question 29

Spectrum of action of macrolides

Answer 29

Nematodes- adult and good larvicides

Arthropods- adults and some immature stages

Question 30

Route of administration of macrolides

Answer 30

Varies with host and drug
Oral, SQ inj, topical
Sustained release: canine heartworm inj, cattle slow release inj

Question 31

Withdrawal times for macrolides

Answer 31

Meat- zero to weeks depending on drug

Eprinomectin, moxidectin for lactating cows have no withdrawal but others can’t be used in lactating dairy animals

Question 32

Safety of macrolides

Answer 32

In general, wide safety margin
Mammalian toxicity probably related to GABA synapses but generally don’t reach targets in vertebrate CNS
Signs include dilated pupils, ataxia, confusion, depression, collapse
Two specific concerns: ivermectin in dogs and moxidectin in horses and dogs

Question 33

Concerns about ecotoxicity of macrolides

Answer 33

On beneficial arthropods

On aquatic organisms

Question 34

What breed of dog is there a special concern for regarding ivermectin?

Answer 34

Collie type breeds

Question 35

Safety of moxidectin in horses

Answer 35

problems when introduced- mostly improper use
follow label directions
don’t use in young foals, debilitated horses

Question 36

Spectrum of action of isoquinolones

Answer 36

tapeworms and some flukes

safe and effective

Question 37

Cyclic octadepsipeptides

Answer 37

Emodepside is the only one currently marketed in US for cats (profender)
Mode of action: stimulates specific neuromuscular receptor that cuases flaccid paralysis
Spectrum: nematodes
Safety: good

Question 38

Benzenesulfonamides

Answer 38

Clorsulon: treatment for bovine liver fluke in US, most often sold in combo with ivermectin (ivomec plus), not for lactating cattle

Question 39

Melarsomine

Answer 39

Immiticide

Arsenical used for heartworm treatment

Question 40

Piperazine

Answer 40

used mostly for ascarid nematodes; paralyze worms, anticholinergic
available in wide variety of OTC products

Question 41

Amino acetonitriles

Answer 41

New drug
Mode of action: act at nematode specific acetylcholine receptor on muscle, hypercontraction of body and spasmodic contraction of pharynx
Spectrum of action: nematodes, effective against nematodes resistant to other anthelmintics
Monepantel will probably reach US in a few years for food animals