23. Antiparasitics Flashcards
What is the general treatment and control goals and principles of antiparasitics?
want to kill and remove life cycle stages (adults and larvae) infecting DH
We want to prevent or reduce prod of parasite offspring (eggs and larvae)
want to minimize enviro to prevent transmission (pick up feces)
Want to optimize DH health to resist infection
We want to prevent DH contact with any IP hosts
Want to neutralize any IP hosts
Assess risk factors for each patient/herd to determine best practices
Judicious use of parasiticides is critical to avoid creating resistance
Prevention of infection, where possible, is preferable to tx and infection
What are most antiparasitics used todaY?
neurotoxins
designed to target specific receptors on neurons within parasite
these receptors work differently in mammals and birds, or are not present, and therefore generally safe for the host
What are the main groups of anthelmintics?
macrocyclic lactones (endectocides)
Benzimadazoles
Tetrahydropyrimidines - pyrantel/morantels
Misc - levamisole, piperazines, emodepside
Isoquinolones - praziquantel, espirantel
What are macrocyclical lactones
Safe and highly effective
nematodes and arthropods - oral, in-feed, injectable, pour-on (transdermal)
This class of drugs is used in all hosts
Systemic - so some products will kill tissue stages
Where did macrocyclic lactones originate from?
All structurally similar - complex chemicals originated from bacteria (some have been enhanced synthetically)
like most antiparasitics, they are neurotoxins - in parasites, the tx results in a flaccid paralysis
Worms can’t stick around in the gut if they can’t move
What is ivermectin?
1st macrolide available in vet med - from a bact
Available in oral, injectable, pouron
Wide spectrum - endectocide (only kills nematodes and arthropods), heartworm prevention, GI nematodes, external parasites
Widely used in many species (sm anim, LA, exotics, people) on and off label
Commonly combined w/ other antiparasitics to prod a prod w/ a very wide spectrum of activity
How are solamectin, doramectin, eprinomectin, milbemycin oxime and moxidectin similar?
all have similar MOA as ivermectin
Highly effective, oral, injectable, topical
used in all hosts to treat or prevent a variety of infections/infestations (nematodes and arthropods)
A number are used as heartworm preventatives
in food anims al have specific WDT
are macrolides toxic?
generally safe with a fairly selective toxicity and high TI
Can prod toxicity (neuro signs) in susceptible anims or w/ significant overdose
OD or genetic MDR1 mutation allows it to cross BBB into brain to cause hypersalivation, vomiting, ataxia/staggering
progresses to bradycardia, unresponsiveness, mydriasis, loss of menace response, and eventually coma
What is the MDR1 genetic defect?
MDR1 has multidrig resistance 1 gene
primarily collies, australian sheperds, and other breeds
If vet is worried, genetic testing available
What are benzimidazoles?
Antinematodal, antitrematodal, anticestodal and antiprotozoal activity
Thiabendazole, fenbendazole, albendazole, febantel, triclabendazole
used in SA and LA, primarily oral
WDT
How do benzimidazoles work?
Act by attacking special proteins in the parasites called B-tubulin
Disrupts normal cellular function and kills parasites
mammals have B-tubulin, but it differs from the parasites - generally wide margin of safety (selective toxicity)
however, rapidly dividing mammalian cells may be affected (rely heavily on B-tubulin)
Teratogenic effects @ high does
resistance becoming a problem
What is pyrantel?
initial spastic contraction followed by paralysis and death, nematodes primarily
What is emodepside?
for cats for nematodes and cestodes, topical application
What is piperazines?
common in LOTS of OTC products
narrow spectrum of activity
How can we kill heartworm?
adulticide - melarsomine - only drug to kill adults, not effective against microfilariae or L3 larvae
Microfilaricides - drugs used to kill the circulating microfilariae in dogs prior to or post tx w/ an adulticide - most often a macrocyclic lactone
heartworm preventatives - drugs used to kill larvae introduced to a dog by a mosquito (most often a macrocyclic lactone), plus these are often within combination products that also incorporate tapeworm and ectoparasite tx
in areas of high endemicity, also evidence of nematode resistance to these preventatives
