Parasitic Drugs Flashcards
Treating cestode tissue cysts
NOTHING
Benzimidazoles
-benzene ring +imidazole ring= benzimidazole
-works on GI (and some lung) nematodes, some cestodes in GI and trematodes in liver
*less on trematodes because drug stays mostly in the GI which is not where the flukes are
Benzimidazole mechanism of action
Binds to parasite beta-tubulin subunit of microtubule
-disrupts parasite cell shape, division, motility, secretion, absorption
*also binds to mammalian tubulin but dissociates quickly so little effect
*efficacy linked with increased drug-parasite exposure time
Negative effects of Benzimidazole
Generally safe
-bone marrow hypoplasia and pancytopenia reported after high/prolonged dosing in dogs
Benzimidazole Absorption PK
-poorly water soluble (pastes, suspensions, granules)
-poor oral availability
>limited by solubility in GI tract and therefore stay in GI
>Ruminants= drugs go to rumen as reservoir; slowly released to intestines
Benzimidazole Distribution PK
Generally high but variable
Benzimidazole Metabolism and Excretion PK
Metabolism:
- hepatic (CYP enzymes)
-1st pass effects if oral absorption occurs - Other tissues (lung, intestines)
Fenbendazole formulations
Fenbendazole (Panacur)
-DIN number, so can be used off label
-Horses: suspensions, pastes, granules
-Cattle: suspensions, feed premixes
-Swine, chickens, turkeys: Panacur
-Dogs: Panacur granules
Fenbendazole uses
-wide range of nematodes
-strongyles, ascarids, whipworms, hookworms, pinworms
-cestodes (Taenia claim in dogs
Fenbendazole off label use
-Small ruminants (sheep and goats)
-Cats: nematodes, giardia, lungworm (Aelurostrongylus)
-Birds, reptiles, exotics
Febental
-fenbendazole pro drug
-led to Drontal Plus (febental, pyrantel, praziquantel for tapeworms)
Albendazole
-Tradename= Valbazen
-oral suspension for cattle
-used for some adult flukes (Fasciola hepatica), adult cestodes, GI and lung nematodes
**gets into bloodstream..probabily why it works with flukes BUT
**potential teratogenic early in gestation… don’t use within 21 days of breeding
Triclabendazole
-Tradename= Fascinex
-active against adult and juvenile F.hepatica AND other flukes (F. magna, Paragonimus)
**juveniles are the ones making tracts through liver
Not licensed in Canada, but possible for Emergency Drug Release
Emergency Drug Release
to permit the manufacturer of a new drug to sell a limited quantity of the new drug to a vet
*used for diagnosing or treating a medical emergency
Foreign drug eligibility for foreign drug release
- medication used to treat serious disease
- medication not marketed in Canada
- documented clinical efficacy and target animal/human safety data are available (not just reports from VIN)
- there are no comparable products available
What products are not available foe emergency drug release?
-Biologics (vaccines or antitoxins)
-investigational drugs not approved elsewhere
-products where there are comparable product in Canada. *cost and ease of use and not valid reasons
-not used for pharmaceutical companies circumventing vet drug approval process
Macrocyclic lactones
-Avermectins
-Milbemycins
*endectocides (kill both internal and external parasites
*related to macrolide antibiotics but no real antimicrobial activity
-come from Streptomyces in soil
Avermectins
-Ivermectin
-Selamectin (small animal)
-Eprinomectin (dairy cows, but no access to milk)
Milbemycins
-Moxidectin
-Milbemycin
Macrocyclic lactone mechanism of action
-Activate glutamate-gated Cl channel allowing Cl entry
-causes flaccid paralysis in worm (pharyngeal muscles and somatic muscles). They let go and are flushed out
Macrocyclic lactone effect on mammals
-At high concentrations, may bind with GABA receptors causing flaccid paralysis issues
Macrocyclic lactone use
-used for nematodes and arthropods.
*no cestodes or trematodes
*no Demodex mites, or adult heartworm
-heartworm prevention (very small dose needed to prevent and work against larvae)
Macrocyclic lactone PK
-oral, topical, injectable products
*note: pour ons on cows, means others non treated will also receive orally when they lick each other
-oral or transcuticular absorption by parasite
-lipophilic, high VD, wide distribution in tissues
-hepatic metabolism, mostly excreted via bile/feces
-elimination half life: 1-3 weeks
*watch withdrawal times (very long)
*will go to milk
