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23 – Parasiticides I Flashcards

1
Q

Basic principles of parasiticides

A
  • Need to have a good idea of what you are treating
    o Life cycle
    o Parts of life cycle that can’t be treated
  • Need to know duration of treatment if you want to eradicate
  • *management
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2
Q

Benzimidazole mechanism of action

A
  • Binds to parasite beta-tubulin subunit (microtubule)
    o Disrupts parasite cell shape, division, motility, secretion, absorption, etc.
    o Binds to mammalian tubulin too, but dissociates quickly=little effect
  • *increase drug-parasite exposure time correlates with efficacy
  • (microtubule disruptors in chemo drugs)
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3
Q

Benzimidazole generally safe in mammals: one example in dogs with prolonged dosing in dogs

A
  • Bone marrow hypoplasia and pancytopenia reported after PROLONGED DOSING in puppies at high doses
  • *generally not many side effects
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4
Q

Benzimidazole spectrum of activity

A
  • BROAD SPECTRUM ANTIHELMINTICS
    o GI and lung nematodes (roundworms)
    o Some cestodes (tapeworms) and trematodes (flukes: minimal as in liver and not much exposure happens there)
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5
Q

Differences in anthelmintic activity between benzimidazoles is likely due to differences in

A
  • PK (ie. Absorption and distribution)
  • *anthelmintic potency generally similar
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6
Q

Benzimidazole PK: absorption

A
  • Generally poorly water-soluble
    o Formulations: pastes, suspensions, granules
  • Usually poor ORAL bioavailability
    o Limited by solubility in GI tract (fine for GI roundworm efficacy)
    o Works well in ruminants: rumen is a reservoir and then slowly released into intestines
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7
Q

Benzimidazole PK: distribution

A
  • Generally high (but variable)
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8
Q

Benzimidazole PK: metabolism and excretion

A
  • Extensive HEPATIC metabolism (CYP enzymes)
    o 1st pass effects if oral absorption does occur
  • Also metabolism in lungs and intestines
  • *metabolites have varying levels of activity
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9
Q

What are some benzimidazole formulations?

A
  • *Fenbendazole (ex. Panacur, Safe-Guard)
  • Febental
  • Albendazole
  • (NOT in Canada: Triclabendazole)
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10
Q

Fenbendazole is licensed for use in

A
  • Horses (suspensions, pastes, granules)
  • Cattle (suspensions, feed premixes)
  • Swine, chicken, turkeys (Gel or Safe-guard mix)
  • Dogs (panacur granules)
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11
Q

What are the label claims of Fenbendazole?

A
  • Wide range of NEMATODES (especially adult GI worms, lung worms)
    o Strongyles, ascarids, whipworms, hookworms, pinworms, etc.
    o Cestodes: Taenia claim in DOGS
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12
Q

Fenbendazole is commonly used OFF-LABEL in

A
  • Small ruminants (sheep and goats)
  • Cats
  • birds/reptiles/other exotics
  • *can be used as it has a DIN
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13
Q

Fenbendazole off-label use in cats

A
  • used for variety of nematode infections, Giardia
  • popular choice for clinical disease associated with lungworm (Aelurostrongylus)
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14
Q

Febental

A
  • fenbendazole pro-drug
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15
Q

Drontal plus:

A
  • Febental, includes pyrantel (just another general dewormer) and praziquantel (specific for tapeworms)
  • licensed for use in dogs
  • *’general dewormer’
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16
Q

Albendazole (Valbazen)

A
  • oral suspension licensed for use in cattle
  • *do get into the blood stream (likely why some fluke activity)
  • possible teratogenic early in gestation (don’t use within 21 days of breeding)
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17
Q

Albendazole (Valbazen) indications

A
  • some ADULT flukes (Fasciola hepatica)
  • ADULT tapeworms
  • Same GI and lung adult round worms as Fenbendazole
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18
Q

Triclabendazole (Fascinex)

A
  • Like albendazole with Cl- attached
  • Active against adult and JUVENILE F. hepatica
  • Active against F. gigantica, F. magna and Paragonimus (lung fluke)
  • *gets flukes super well but not other things (gets all stages!)
  • NOT licensed in Canada
    o Emergency drug release
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19
Q

What is an emergency drug release?

A
  • Authorization to permit the manufacture of a new drug to sell a limited quantity of new drug to veterinarian
    o Not marketed in Canada
    o Requested by practitioner for purpose of diagnosing or treating a medical emergency
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20
Q

What are the foreign drug eligibility criteria for an emergency drug release?

A
  • Medication used to treat/diagnose and SERIOUS disease condition
  • NOT marketed in Canada
  • Documented clinical efficacy and target animal safety data are available for product
  • No comparable products available for effectively diagnosing/treating the condition
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21
Q

What products are NOT eligible for an emergency drug release?

A
  • Biologics are not approved by Health Canada
  • Investigational drugs that are not approved in other jurisdictions
  • Products where a comparable product is currently marked in Canada
    o Cost and ease of use are NOT consider valid reason for requesting EDR
  • *not meant for a way for a company to circumvent the vet drug approval process
22
Q

Macrocyclic lactones

A
  • Related to macrolide antibiotics
  • Produced by fermentation by Streptomyces in soil
  • Considered endectocides
    o Kill BOTH internal and external parasites
23
Q

What are the 2 macrocyclic lactone groups?

A
  • Avermectins
  • Milbemycins
24
Q

What are examples of Avermectins?

A
  • Ivermectin
  • Selamectin
  • Eprinomectin
  • (Doramectin)
  • (Abamectin)
25
What are examples of Mibemycins
- Moxidectin - Milbemycin
26
Macrocyclic lactone mechanism of action
- *Activates (opens) glutamate-gated Cl- channel - Cl- entry into cell (hyperpolarization) - Flaccid paralysis in worm o Pharyngeal muscles: can’t ingest nutrients o Somatic muscles: can’t move - May bind with GABA receptors at high concentration - *NEUROTOXIN ON PARASITES
27
Macrocyclic lactones are effective against
- Nematodes and arthropods o Exceptions: demodex mites, some ADULT filaria (heart worm) less susceptible o Heartworm prevention dose is very low (1-10% of typical dose) - *differences in activity and potency between them
28
Macrocyclic lactones spectrum of activity
- Effective against most nematodes and arthropods - Minimal activity against cestodes and trematodes - Oral or transcuticular absorption of ML by parasite from the treated host animal
29
Macrocyclic Lactone PK
- Oral, topical or injectable products o Topical can be oral too=transfer by grooming (ex. cows) - Generally lipophilic: high volume of distribution (especially MOXIDECTIN!) - Some hepatic metabolism, mostly excreted via bile/feces - Elimination half-life 1-3 weeks
30
Macrocyclic lactone elimination half life: 1-3 weeks
- Watch withdrawal times: typically very long - *Milk: not licensed for diary cows (except moxidectin and one formulation of eprinomectin)
31
What are the adverse events of macrocyclic lactones?
- Generally safe, but when AE do occur=more significant then benzimidazoles - Toxicity: associated with GABA stimulation in CNS o Treatment=supportive care (fluids, oxygen, etc) (IV lipid emulsion?) - Normally little distribution to CNS, but exceptions
32
Exceptions of macrocyclic lactones that have more distribution to the CNS
- ABC-B1 mutant dogs (‘white feed, don’t treat’) - Decrease P-gp function=increase distribution into brain
33
Ivermectin (Ivomec=pioneer drugs, but many generics available) ‘solutions’
- Oral drench: sheep - Oral paste: horse - Injectable: cattle, sheep, swine - Oral premix: swine - Oral tablet: dogs (*heartworm prevention with pyrantel) - *withdrawal for meat and MILK (long time) - *good for round worms, no activities on tape worms
34
Eqvalan gold paste
- Ivermectin - With praziquantel: for tapeworms - *be skeptical of drug marketing (duration?)
35
Heartgard
- First prevention for heart worm - Very LOW ivermectin content for heart worm prevention - Pyrantel: more of the dewormer
36
Eprinex Pour On (Eprinomectin)
- Similar compound to Ivermectin - Licensed for use in dairy cattle with NO MILK WITHOLDING TIME o Has Maximum Residue Limit (MRL) in milk o Unlike ivermectin (no MRL for milk in Canada) - *not licensed for GOATS
37
Ivomec and Eprinex by same company
- Look similar - *need to clarify=if wrong product=dump milk for 2 months!
38
Long range (Eprinomectin)
- Extended released SC injection - 2 different solvent carriers: rapid and slow absorption - 4-5 month activity against some worms - 4 month meat withdrawal period - *NOT FOR USE IN DAIRY COWS
39
Revolution (Selamectin)
- Monthly topical formulation for cats and dogs (SMALL ANIMAL) - *Less affinity for P-gp than ivermectin o Safer for ABC-B1 mutants: not necessarily ‘safe’ - Interest for use in aquaculture: fee premix for control of sea lice in salmonids
40
What are some uses of revolution (selamectin)?
- Fleas - (Ticks: efficacy is limited, still bitten) - Mites - Nematodes (hook and round worms) - HEARTWORM PRVENTION - *topical and gets into systemic circulation
41
Moxidectin ‘types available’
- Quest/Quest Plus oral gel: horses - Advantage multi (monthly topical: dogs, cats, ferrets) - ProHeart 6 (sustained release injection) - With various isooxazoline formulations - *good for treating mange
42
Quest/Quest plus oral gel (horses)
- Moxidectin +/- praziquantel - All kinds of nematodes +/- tapeworms
43
Advantage multi (monthly topical)
- Moxidectin + imidacloprid - Heartworm prevention - Fleas, ear mites, GI nematodes
44
ProHeart 6
- Heart work prevention for 6 months
45
Milbemycin in small animals: monthly tablets
- Milbemax tablets: cats - Interceptor tables: dogs and cats - Sentinel tablets: dogs - Trifexis tablet: dogs - Nexgard spectra: dogs - *all get the same things
46
Milbemycin tablets treat/prevent
- Heartworm prevention - Hookworm - Round worm - Tapeworm - Whipworm
47
Macrocyclic lactone resistance
- Huge problem in sheep - Emerging in cattle/horses - *widely reported in cyasthostomes and small strongyles - *ex. hemonchus
48
What are the resistance mechanisms?
- Induction of parasite efflux pumps (ex. P-gp) - Changes in Glu-gated Cl- channels
49
How do you test for resistance parasites?
- Fecal egg count reduction o Pre- and post- treatment fecal egg counts o Resistance if not at least 95% reduction in counts
50
Macrocyclic lactones ecological impact
- Persist in feces for a long time o Can kill insects that degrade feces (ex. dung beetle) - Evaluate as part of drug approval process - *don’t dissolve out of feces (don’t need to worry about water contamination)
51
How might you change the PK properties to mitigate the potential risk of ecological impact of macrocyclic lactones?
- *excreted in different form or completely metabolized by liver
52
Macrocyclic lactones: topical tips
- Apply to SKIN: not hair - Watch for skin/hair condition (ex. mud/feces) - Decreased efficacy if applied at very low temperatures - Flammable (watch out while branding!)

PHARMACOLOGY - 2 (16 decks)

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