Antiparasitics

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2getAs
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83665
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Antiparasitics
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2011-05-04 00:21:48
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Antiparasitics Veterinary Pharmacology
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Veterinary Pharmacology
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  1. Parasite
    organism that lives in or on another organism at its expense
  2. Ectoparasites
    live on surface of animal's body; like ticks; cause infestations
  3. Endoparasites
    live inside the animal's body; cause infections
  4. Diagnosis of parasites
    • - sometimes on surface of animals
    • - other times need to exam a fecal sample (eggs/larvae released in feces)
  5. Ideal parasiticide
    • - selectively toxic
    • - no resistance
    • - economical
    • - effective against all stages
  6. Helminths
    • - drugs that treat= antihelminthics
    • - include nematodes and platyhelminths
    • - not protozoa
  7. Nematodes
    • - cylindrical and nonsegmented
    • - generally inhabit GIT
    • - filarial nematodes are a special group
  8. Platyhelminths
    • - flat worms
    • - include cestodes (tapeworms) and trematodes (flukes)
  9. Protozoa
    • - single cell, not helminth
    • - include coccidia, toxoplasmosis
  10. Routes of infection of hookworms
    • - infective larvae penetrate skin
    • - infective larvae enter host transplacentally
    • - host ingests infective larvae in food, colostrum, or milk
  11. 6 groups of antinematodal drugs
    • 1. benzimidiazoles
    • 2. tetrahydropyrimidines
    • 3. piperazines
    • 4. organophosphates
    • 5. imidazothiazoles
    • 6. macrocyclic lactones (macrolides)
  12. Benzimidazoles
    • - include thiabendazole (has some antifungal properties), oxibendazole (equine past deworm), fenbendazole (Panacur), albendazole, Febantel (pro benizimadole)
    • - low toxicity
    • - attacks proteins necessary for cell divisions in parasites
    • - problems with resistance
    • - targets microtubules of all
    • - liquid gran powder past
  13. Tetrahydropyrimidines
    • - pyrantel- 2 forms
    • - suspension
    • - highly effective against hookworms and roundworms
    • - only targets adults
    • - classified as cholinergic agonist
    • - parasympathomimetic ( targets ACh neurotransmitter, contractions)
    • - if parasite is freely living and not attached it will be expelled
    • - only acts within GI tract
    • - also used in people with pinworms; horses get pinworms too
  14. Piperazines
    • - GABA agonists
    • - OTC
    • - roundworms
    • - narrow spectrum
    • - normal side effect: bolus of worms through vomit or defecation
    • - MA: pump protein--> pump out Cl- --> into cell depolarize --> expel worm
  15. Organophosphates
    • - used for ectoparasites
    • - narrow range of safety
    • - MA by irreversibly inhibiting acetylcholinesterase
    • - end up with cholinergic signs: paralysis
    • - cats more prone to OP toxicity-- dip
    • - antidote for toxicity = atropine
    • - used a lot in large animal pour-ons, powders
    • - cholinergic crisis = salivation, lacrimation, urinating, diarrhea
  16. Imidazothiazoles
    • - only levamisol in large animals
    • - cholinergic agonist; stimulating --> paralysis
    • - same toxic side effects as OP
    • - used in poultry
  17. Macrocyclic lactones (macrolides)
    • - endectocide; broad spectrum against nematodes and get ectoparaistes like mites and lice
    • - include avermectins and milbemycins
    • - not effective against cestodes or trematodes
    • - MA: induce spastic paralysis through GABA receptor at high concentrations
    • - some effect at glutamate ion channels: hyperpolarization of parasite; muscle spasms; cannot move; parasites are washed away or attacked by immune cells
    • - cause paralysis of pharygeal muscles of parasites
    • - worms lack CNS
  18. Acaricide
    • - kills mites by paralyzing pharyngeal muscles
    • - toxicity causes mutation of transporter proteins
    • - accumulation = hyperpolarization and neurological problems
    • - ivermectin hazardous to collies, australian shepherds, and sheep dogs
  19. Heartworm
    • -once/month preventative = low dose; not effective for L1/L4
    • - significant disease in right side of heart leading to CHF
    • - diagnosed by snap test or x-ray through enlargement of right side of heart
    • - expensive to treat= arsenic cmpds for adult worms; restrained for 1-2 months to prevent thromboembolism
    • - treatment also depends on if microfilaria is being produces
  20. Immiticide
    heartworm adulticide; deep intramuscular injection (back muscles)

    - melarsomine dihydrochloride
  21. Treat microfilaria after 1-2 months of clearing adults with
    macrocyclic lactones at high doses (extra label)

    there is a risk of neurotoxicity with no antidote
  22. Ivermectin
    antinematidal in large animals; given by injection and in horses given orally only
  23. Resistance
    occurs when a greater # of individuals in a population are resistant or no longer affected by the medication; permanent
  24. Cestodes (tapeworms)
    • - affects both small and large animals
    • - not affected by macrocyclic lactones
    • - thin end (head); proglottins (segments) packed full of eggs and passed in feces when shedding
    • - each egg has immature head of tapeworm
    • - suckers on head attach to mucosa of sm. intestine and absorb nutrients
    • - parthenogenesis (need no mate)
    • - infection through ingestion
  25. Anticestodal drugs
    • - attack the attachment site (scolex= head), causing paralysis, and worm gets purged through feces
    • - causes an increase in calcium ion permeability, parasite loses calcium with is necessary for muscle contraction and relaxation
    • - includes Praziquantel (Droncit), Epsiprantel (Cestex)
    • - oral tablets
  26. Trematodes (flukes)
    • - fasciola hepatica
    • - great economic impact in cattle
    • - unsegmented parasitic flat worms, visible to naked eye (1 cm in length)
    • - lead to liver condemnation, unthriftiness and loss of condition in cattle
    • - cysts in liver, adults reside in these cysts
    • - intermediate host = snail
    • - ingestion when grazing on pastures near ponds or natural water supply
  27. Anti-trematodals
    • - includes praziquantel (used in sm animals to treat lung flukes), albendazole, and curatrem (colorsulon; main)
    • - inhibits the energy production system of these parasits (glycolysis)
    • - given by drench (oral solution)
  28. Protozoans
    class of organisms, single celled, eukaryotic

    include giardia, coccidia, and sarcocystis neurona
  29. Coccidia
    • - intestinal protozoa; causes GI problems in young animals, diarrhea, scours in calves
    • - problem in poultry
    • - prevent by decreasing stocking #'s and increasing sanitization
    • - parasite invade cell that line sm intestine, replicate, cell ruptures, release in lumen, infect other cells, and cells are not able to absorb nutrients which causes the diarrhea
    • - treat with coccidistats: monensin which effects metabolism of protozoa
    • - narrow spectrum: corid (amprolium) in large animal and sulfa antibiotic (albon) in cats and dogs
  30. Giardia
    • - zoonotic disease, infect sm. intestine, epithelial stage
    • - have flagella
    • - diagnose with fecal elisa tests
    • treat with fembendazol (panacur)
    • - can treat with antimicrobial agent= flagel (metronidazole) but not approved yet; can lead to nausea/vomiting at high levels (neurotoxin); unpalatable for cats, effective against anaerobic microbes
  31. Sarcocystis neurona
    • - protozoal disease cusing EPM (equine protozoal myolitis)
    • - affects CNS of host
    • - intermediate host = armadilos, raccoons, skunk
    • - Definitive host = opposums
    • - Dead end host = horse
    • - drug: ponazuril which inhibits nuclear division in parasite (cocciostatic)
    • - EPM: nurological signs, prevalent, muscle atrophy, lameness, CSF test, expensive
  32. Antiprotozoals
    • - Albon (sulfadimethoxine)
    • - Panacur (fenbendazole)
    • - Flagyl (metronidazole)
    • - Marquis (ponazuril)
  33. Treat Ectoparasites with
    • - Organophosphates and carbamates
    • - pyrethrins and pyrethroids
    • - macrolides
    • - imidacloprid
    • - frontline (Fipronil)
    • - capstar (nitempyram)
    • - program (lufeneron)
    • - mitaban, preventic (amitraz)
  34. Organophosphates and carbamates
    • - Developed as nerve gas originally
    • - Dips
    • - Toxicity signs: (parasympathetic over stimulation), Hypersalivation, Defacation, Pupils dilation (mydriasis), Epiphora, will progress to muscle tremors/seizures

    • - Mechanism of action: irrevesibly inhibit acetylcholinesterase causing paralysis; parasite falls off or is destroyed
    • - Cats very sensitive; Antidote: atropine
  35. Pyrethrins and Pyrethroids
    • - safe; applied external (spray or dip)
    • - Pyrethrins: natural products, toxic to fish, not a good kill effect on adults but great knockdown effect; MA: open Na+ channels in insects causing hyperpolarization

    - Pyrethroids: synthetic; used as a room defogger to kill larval stages; cant penetrate eggs; good kill effect; can cause toxicity in cats; use on adult animals

    - Insect growth regulators to prevent molting can be added--- mimic effect of juvenile growth hormone
  36. Macrolides
    • - Include selomectic (active ingredient in Revolution)
    • - In ruminants by injection; horses= paste; drench; topically
  37. Imidacloprid
    • - Topically-- between shoulder blades; not absorbed systemically; Trifexis
    • - Advantix in dogs has pyrethrin added; Advantage in cats
  38. Fipronil
    • - Not absorbed systemically
    • - Interferes with nicotinic insect receptors
    • - Gets into sebaceous gland --> 30 day absorbed
    • - Nontoxic even if animals accidentally ingest
    • - Alopecia or hair loss at site
    • - Need a couple days to be absorbed and avoid touching area
  39. Nitempyram
    • - oral
    • - Kill adult fleas; absorbed systemically
    • - Animals have to get bitten
    • - Works well for maggot infestation in animals
    • - Can be used in fly-strike in rabbits
  40. Lufeneron
    • - chewable tablet
    • - Inhibits insect growth by interfering with chitin
  41. Amitraz
    • - Preventic collar --> if ingested causes coma and lead to death; trim excess collar
    • - Mitaban dip-- only approved product to treat demodectic mange in dogs (not all dogs respond to it); caused by demodex canis

    • - CANNOT BE USED IN CATS
    • - Miticidal; effective against ticks too
    • - Highly toxic if ingested
    • - Staff must wear personal protective equipment
    • - Alpha2 receptor agonist (depresses norepinephrine)
    • - See depression and sedation
    • - MAO inhibitor (recycling norepi)
    • - Antidote --> yohimbe
    • - Milbomycin works better than ivermectin
  42. Mange
    • - Demodectic: Live in hair follicles; causes hair loss; inflammation; severe skin infestation; bacterial infection; Genetic: neuter or spayed a must
    • - Another type of mange is sarcoptic mange: burrows under skin into dermis; treat with ivermectin

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