Parasitology slide set 2 Flashcards
Trends in development of vet parasiticides
Broad spectrum
ease of application
antiparasitic drugs
called anthelmintics
most widely used are the “modern anthelmintics”
“Modern” anthelmintics
developed sine 1960
broad spectrum
high safety margin
Members of the benzimidazoles and probenzimidazoles
fenbendazole (horse, cow, goat, pig, dog)
albendazole (sheep, cow, goat)
oxibendazole (horse)
oxfendazole (horse, cow)
febantel (dog, once metabolized becomes fenbendazole)
Mode of action of benzimidazoles and probenzimidazoles
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
Members of tetrahydropyrimidines
pyrantel
morantel
Mode of action of tetrahydropyrimidines
acetylcholine agonist
Member of imidazothiazoles
levomisole
Mode of action of imidazothiazoles
acetylcholine agonist
Members of avermectins/milbemycins (aka macrolides or macrocyclic lactones)
Avermectins: ivermectin doramectin eprinomectin selamectin Milbemycins: moxidectin milbemycin
Mode of action of avermectins/milbemycins (aka macrolides or macrocyclic lactones)
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)
Members of isoquinolines
praziquantel
epsiprantel
Mode of action of isoquinolines
affects cell membrane permeability; tetanic contraction of muscles probably related to changes in permeability of tegument to calcium
Side resistance
if resistant to one member of a group, resistant to all members of the group
Important in benzimidazoles and macrolides
Cross resistance
occurs when resistance to one group confers resistance to another group; don’t see this much
Imidithiazoles and tetrahydropyrimidines
Spectrum of action of benzimidazoles
Nematodes- adult, most are larvividal (but may need to increase dose)
Tapeworms and flukes- albendazole and fenbendazole have some activity
Administration of benzimidazoles and probenzimidazoles
oral only, poorly water soluble
Withdrawal times for benzimidazoles and probenzimidazoles
Meat withdrawal days to weeks
Milk withdrawal- none with fenbendazole, others are not approved for lactation or have withdrawal
Safety in benzimidazoles
Usually very safe
Exceptions: albendazole- ruminants in early pregnancy; febntel- dogs during pregnancy
Benzimidazole resistance in US
Cases described in: strongylid nematode parasites in horses, small ruminants, and cattle
Also for equine ascarids (roundworms)
There is cross resistance between imidazothiazoles and
tetrahydropyrimidines; specifically levamisole, pyrantel, morantel
Mode of action of levamisole, pyrantel, morantel
Cholinergic agonists- depolarizing neromuscular blocking agets
Rapid, reversible spastic paralysis of worms, eliminated by normal gut activity
Administration of levamisole, pyrantel, morantel
primarily oral
Withdrawal time of levamisole, pyrantel, morantel
Meat- days
Morantel- no milk withdrawal, others not approved for lactating food animals
Spectrum of action of levamisole, pyrantel, morantel
Adult nematodes
Pyrantel used for horse tapeworms in the past
Safety of levamisole, pyrantel, morantel
Good, levmisole associated with most problems- might see salivation, tremors usually in small ruminants
Resistance described for levamisole and pyrantel
Levamisole- small ruminant strongylids
Pyrantel- horse strongylids, ascarids
Generally assume cross resistance of imidithiazoles and tetrahydropyrimidines
Macrocyclic lactones (macrolides) general info
Called endectocides b/c have activity against internal and external parasites
Originally fermentation products of soil microbes
Spectrum of action of macrolides
Nematodes- adult and good larvicides
Arthropods- adults and some immature stages
Route of administration of macrolides
Varies with host and drug
Oral, SQ inj, topical
Sustained release: canine heartworm inj, cattle slow release inj
Withdrawal times for macrolides
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
Safety of macrolides
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
Concerns about ecotoxicity of macrolides
On beneficial arthropods
On aquatic organisms
What breed of dog is there a special concern for regarding ivermectin?
Collie type breeds
Safety of moxidectin in horses
problems when introduced- mostly improper use
follow label directions
don’t use in young foals, debilitated horses
Spectrum of action of isoquinolones
tapeworms and some flukes
safe and effective
Cyclic octadepsipeptides
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
Benzenesulfonamides
Clorsulon: treatment for bovine liver fluke in US, most often sold in combo with ivermectin (ivomec plus), not for lactating cattle
Melarsomine
Immiticide
Arsenical used for heartworm treatment
Piperazine
used mostly for ascarid nematodes; paralyze worms, anticholinergic
available in wide variety of OTC products
Amino acetonitriles
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
