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50 Cards in this Set
- Front
- Back
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What are anthelmintics?
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Chemotherapeutic agents
pharmacologically active compounds that control the parasite without injuring the host SELECTIVE toxicity Compare to vaccines, which stimulate protective immune response Anthelmintics control helminth parasites |
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What anthelmintics are used on Nematodes?
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Macrolytic lactones: Avermectin, Milbemycin
Benzimidazoles Levamisole/Morantel |
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What anthelmintics are used on Cestodes?
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Praziquantel
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What anthelmintics are used on Trematodes (liver flukes specifically)
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Tridabendazole
Salicylanilide |
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What anthelmintics are used on heartworm?
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Arsenicals
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Levamisole/Morantel
Modes of application |
Widely used, cheap, can be oral, injected, or pour on
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Levamisole/Morantel
Spectrum of activity |
Wide spectrum of activity against nematodes
Deficiencies against some larval stages (especially hypobiotic forms) Adults +++ Mucosal Larva + Hypobiotic Larva - |
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Levamisole/Morantel
Safety margin |
Relatively narrow (especially dogs and horses)
Chance of toxicity Relatively low ‘selective’ toxicity |
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Levamisole/Morantel
Mode of action |
Neural and neuromuscular junctions as cholinergic agonist and thereby induces spastic paralysis in nematode worms
Causing them to detach, and pass |
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How can Levamisole/Morantel hurt humans?
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The drug can cause agranulocytosis, which significantly reduces the number of white blood cells in the body causing fever, swollen glands, and painful sores around the mouth and anus. And women seem to be more affected by levamisole than men are.
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Morantel/Pyrantel
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Morantel: ruminant dewormer
Pyrantel: dog/cat/horse dewormer Similar to levamisole, but not absorbed through alimentary tract Pyrantel pamoate is active against hookworms and ascarids and acts as a blocking agent, causing paralysis. This results in the hookworm losing its grip in the intestinal wall and is removed from the pet’s system by natural process. Will miss mucosal larvae, ie: lungworm Adults +++ Mucosal larva - Hypobiotic larva |
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Administration routes of Levamisole/Morantel, peak effectiveness, and duration of effectiveness.
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Injectable- highly effective but short-lasting
Oral-moderately effective, moderate duration. Topical/pour on- least effective, but long lasting. |
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What are the macrolytic lactones?
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Ivermectin/abamectin, doramectin, moxidectin, eprinomectin, selamectin
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Macrolytic lactones: spectrum of activity
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Extremely potent, wide spectrum of activity
Most common nematodes (all stages) Many arthropods (blood sucking or tissue dwelling) Endectocide Will be active against migrating heartworm larva and thus is used as a prophylactic at lower doses ADULTS +++ MUCOSAL LARVAL +++ HYPBIOTIC LARVA +++ ARTHROPODS ++ Not chewing louse |
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What parasites will the macrolytic lactones NOT kill?
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INACTIVE against: trematodes, cestodes, and (at normal doses) adult filarial worms
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Rough coated collies and related breeds are not able to metabolize these anthelmintics and may die from it.
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Macrolytic lactones
EXCEPT: Selamectin, which has been shown to be safe for all breeds. |
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How do macrolytic lactones work on parasites?
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Open invertebrate specific glutamate-gated chloride channels in post-synaptic membrane flaccid paralysis
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Macrolytic lactones: methods of application, effectiveness, and duration of effectiveness.
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Injectable/Oral- effective against adult nematodes, but short lasting.
Topical/pour on- effective against L3 larvae, but not adults, and long lasting. |
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What are the main Benzamidazoles?
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Albendazole, fenbendazole, oxfendazole
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BZDs- spectrum of activity
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Broad, effective against adult and developing nematodes, but variable efficacy on hypobiotic larva
Some have limited usefulness against tapeworms Albendazole active against liver fluke Albendazole and fenbendazole also active against Giardia |
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Triclabendazole- what is it effective against? What is it not effective against?
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UNIQUE: highly potent against Fasciola
Useless for nematodes or cestodes |
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BZDs- how do they work against parasites?
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BZD binds to tubulin (basic building block for microtubular structure)
prevents ‘building’ of microtubule structure disruption of microtubular structure of intestinal/tegumental cells glucose uptake reduced glycogen depleted slow death |
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BZDs- are they safe?
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Some can be teratogenic and should not be used in early pregnancy
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BZDs- dose, effectiveness and duration
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BZDs are not dependent upon a peak, but rather duration of exposure inside the body.
BZDs with high solubility are less potent because the body breaks them down more quickly and there is less exposure the the parasites. Multiple low doses better than Single high dose. Reduce feed for ruminants, increase food with dog/cat/pigs. |
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Praziquantel
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Highly effective against Cestodes.
Acts by inducing Ca influx across parasite tegument immediate muscular spasm unable to remain attached swepted away from predilection site by perastalsis Tegument continues to disrupt antibodies, immune cells, and enzymes attack |
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What are the Salicyclanilide Flukicides?
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Nitroxynil, closantel, oxyclozanide
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How do Salicyclanilide Flukicides work against parasites?
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Uncouplers of oxidative phosphorylation
Some are highly toxic |
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What is the only class of anthelmintics that is effective against adult heartworm?
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Arsenicals
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Thiacetarsamide
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"old school" drug used to treat adult heartworm.
Hepatotoxic, nephrotoxic, necrosis at injection site unless goes directly into vein MUST BE VERY CAREFUL |
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Melarsomine
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Modern, safer drug used to treat adult heartworm.
IM injection, usually given 30 days apart Pet is hopitalized for 1-2 days for observation Pain, collapse, sudden death Pet is kept quiet and monitorred closely at home for 30 days |
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What anthelmintic is used to treat heartworm larvae?
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Ivermectin
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Anti-coccidial drugs- what are they used for? Why are they used?
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Major use in broilers and poultry production
Broilers can be batches of 10,000-28,000 Harvest at 35-50 days old This level of productivity can only be maintained if coccidia is adequately controlled Careful management and skillful use of anticoccidial drugs |
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What are the most widely used anti-coccidial drugs?
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monensin, salinomycin, narasin
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Anti-coccidial drugs- how do they control parasites?
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Reduce, but do not eliminate oocyst production in birds
Suppress clinical and subclinical coccidiosis Allow immunity to develop Reduce build up of oocysts |
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Which group of parasites is becoming most resistant to anthelmintics?
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Nematodes, but liver fluke is begining to show resistance also.
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Which group of anthelmintics are parasites becoming most resistant to?
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BZDs
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What is the definition of resistance?
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The ability to tolerate a normally effective dose of a compound.
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What is the definition of tolerance?
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Innate susceptibility
NOT dependent on prior exposure |
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What are the common causes of anthelmintic failure?
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Underestimation of body weight.
-Under dosing Failure to follow instructions. -Ie, shake BZD drench before use. Poor maintenance of dosing equipment. -Incorrect dose given. Rejection of dose. Ie: cats/dogs spit out pill or liquid. Not removing stock from heavily contaminated pasture. Inappropriate choice of drug. -Ie: using Ivermectin for fluke |
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Anthelmintic test: FECRT- fecal egg count reduction test
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It is an In Vivo test that compares fecal egg counts before and 10-14 days after treatment.
It requires 2 farm visits, second visit egg count should be close to zero. Simple, cheap Limitations: Insensitive egg output does not always reflect worm numbers Different species reflected seasonally False negatives – worms are temporarily infertile, but not killed False positives – with drugs with poor activity against mucosal larvae |
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Anthelmintic test: Controlled test
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In Vivo test that involves treatment and slaughter of groups of artificially infected worm-free animals (with appropriate controls)
Reliable but very expensive |
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Anthelmintic test: Egg hatch assay
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In Vitro test where eggs are incubated in serial concentrations of anthelmintic and ED50 value is determined
The concentration at which 50% fail to hatch Useful for BZD resistance |
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Anthelmintic test: Larval development test
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In Vitro test where larvae are incubated in serial concentrations of anthelmintic and rate of development recorded
Takes one week to run Useful for levamisole or ivermectin resistance |
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Anthelmintic test: Tubulin binding test
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In Vitro test useful for detecting BZD resistance.
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Anthelmintic test: Molecular techniques
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RFLP assays and PCR reactions have been developed for BZD resistance
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What 2 main factors does the rate of development of resistance depend on?
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1. Genetic factors
2. Selection pressure |
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What types of genetic factors affect the development of anthelmintic resistance?
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Parasite species
Increased biotic potential increase eggs shed Porportion in refugia less exposure to drug |
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How does selection pressure affect the development of anthelmintic resistance?
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Farm management
Increase stocking rates = increase parasites Anthelmintic usage Increased frequency increased resistance |
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What are the ways to delay the onset of anthelmintic resistance?
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Use an effective drug.
Give correct dose. Use minimum number of doses. Annual alteration of chemical group. -Use different mode of action each year. This reduces side or cross resistance. Don’t introduce resistant worms. -Quarantine and treat all introduced stock. Education and awareness. -Ie: pet/horse owners, farmers. Mix drugs with different modes of action. -Controversial. Use narrow spectrum drugs where possible. Exploiting pharmacokinetic properties to enhance efficacy. -Reduce feed intake of ruminants before dosing. -Give with food for dogs/cats. |
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What are some alternate control strategies to use instead of or in addition to anthelmintics?
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Regular fecal removal.
Enhancing natural immunity and resilience with supplemental feeding. Use of feedstuffs containing natural anthelmintic substances. -Condensed tanins. Use of fungi to reduce numbers of infective larvae developing in feces. -Nematophagous fungi Environmental control of intermediate hosts. -Ie Fasciola, controversial. Copper added to water will kill snails. |
