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Applied Pharmacology > Anthelmintics > Flashcards

Anthelmintics Flashcards

0
Q

How are anthelmintics classified by spectrum?

A

1) endectocides (int. and ext. parasites)
2) narrow spectrum
3) broad spectrum

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1
Q

What are the three factors for efficacy and safety?

A

1) The anthelmintic must target a receptor site on the parasite
2) the receptor site must be unique to the parasite
3) the parasite receptor site must be far more sensitive to the anthelmintic than the host receptor site.

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2
Q

What are the 4 factors that make up group classification?

A

1) Pharmacokinetics
2) Spectrum of activity
3) mechanism of activity
4) adverse effects

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3
Q

What spectrum do benzimidazoles cover and what are 3 examples?

A

They are broad spectrum.
Albendazole, fenbendazole, flubendazole.
I-BZ

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4
Q

What are the pharmacokinetics of Bendimidazoles? (A only)

A 
Insoluble in water.
Oral admin
Poor absorption from the GI tract
Food enhances absorption
Greater plasma levels if longer exposure
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5
Q

Which two benzimidazoles are well absorbed from the GIT?

A

Albendazole and oxfendazole- have good oral bioavailability

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6
Q

What are the pharmacokinetics of Benzimidazoles? (M only)

A

Variable metabolism- most excreted unchanged in the faeces.
Residues occur so they should not be used in lactating animals.
They have active metabolites if they undergo hepatic metabolism e.g. fenbendazole-oxfendazole

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7
Q

What is the mechanism of action of Benzimidazoles?

A

they bind to nematode tubulin and prevent the formation of microtubules. = no protein assembly.
The mammal tubulin- low affinity
Duration of exposure is critical- consecutive dosing for monogastrics.

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8
Q

What is the activity of benzimidazoles in horses?

A

GI roundworms-strongylus, Lung worm.

Broad spectrum and effects adult and larval stages

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9
Q

What is the activity of benzimidazoles in ruminants?

A

Larval and adult stages of GI nematodes, lung worms.

Inhibited ostertagia more difficult to treat- use at induction of inhibition or pre-emergence.

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10
Q

What is the activity of benzimidazoles in pigs?

A

GI nematodes and lung worms.

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11
Q

What is the activity of benzimidazoles in Dogs and cats?

A

GI nematodes, transplacental round worm in dogs, lung worm, taenia (cestode).

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12
Q

What is the difference in effect between triclabendazole and albendazole?

A

1) effective against mature and immature fluke but not nematodes.
2) some efficacy against adult stages.

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13
Q

What are pro-benzimidazoles?

A

e.g. febantel-fenbendazole-oxfendazole
Converted to the active form once metabolised.
They are more water soluble.

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14
Q

What are the adverse effects of benzimidazoles?

A

They are generally safe because the min lethal dose is many times more than the therapeutic dose.

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15
Q

What are the two groups of drug within the macrocyclic lactones?

A

Avermectins and milbemycins.

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16
Q

What are the pharmacokinetics of Avermectins?

A

Administered s/c to cattle for longer t1/2, Distribution depends on the route of admin, Hepatic metabolism, faecal excretion.

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17
Q

What is the advantage of eprinomectin?

A

Excreted unchanged, low milk/plasma coefficient so it is partitioned away from the milk so no withdrawal period is required.

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18
Q

What is the advantage of selemectin?

A

Large amounts are partitioned into the sebaceous glands= acts on ectoparasites and it can be used in collies. (spot on)

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19
Q

What are the pharmacokinetics of Milbemycins- specific examples?

A

Mibemycin oxime- after oral admin, 90-95% is excreted unchanged in the faeces, absorbed drug is excreted in the bile.
Moxidectin is very highly lipophilic= tissue persistence and high distribution, excreted in faeces.

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20
Q

What is the mechanism of action of milbemycins and avermectins?

A

Act on glutamate-gated Cl channels in the parasite.
Or GABA-gated Cl channels
These sites are absent or only in the CNS of the host and the drug will not penetrate the BBB.
NOT COLLIES OR MUURAT GRAY CATTLE

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21
Q

What is the spectrum of activity of Marocylic Lactones?

A

Endectocides- effects nematodes and ectoparasites
No effects on fluke or tape worms as the active sites are absent.
3-ML

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22
Q

How can the macrocyclic lactones be administered?

A

They are highly lipid soluble so: oral, s/c, spot on.

They are long acting.

23
Q

What is the activity of Macrocyclic Lactones in Sheep?

A

i/m, s/c, oral.

GI nematodes and nasal bots.

24
Q

What is the activity of Macrocyclic Lactones in Pigs?

A

i/m, s/c or feed

GI nematodes and Lung worms

25
Q

What is the activity of Macrocyclic Lactones in dogs and cats?

A

Milbemycine oxime for heart worm control- hook worm, nematode, whip worm.
Selemectin spot on for heart worm and nematodes.

26
Q

What are the side effects of Macrocyclic Lactones?

A

Binding of the anthelmintic to GABA related neurones in the CNS of the host. In general they do not cross the BBB but due to deficiency/mutation of P-glycoprotein in collies they should not be used in susceptible spp.

27
Q

What are the differences between selamectin and moxidectin?

A

They are both spot ons but moxidectin will treat larval as well as mature GI nematodes and also the demodex mite.

28
Q

What is the coding for Imidazothiazoles and what are two examples?

A

2-LV, tetramisole and levamisole

29
Q

What are the pharmacokinetics of Imidazothiazoles?

A

Water soluble, rapidly absorbed from the GI tract, injectable and pour on, Levamisole is the L isomer (was racemic mixture) so it is now less toxic. Rapid metab and elim- in both urine and faeces

30
Q

What is the activity of Macrocyclic Lactones in cattle?

A

s/c or pour-on.

GI nematodes, lung worm and type II osteragiasis

31
Q

What is the mechanism of action of the imidazothiazoles?

A

They effect the nervous system of the parasite- act at ACh/nicotinic receptors in the ganglia of the parasite=reversible contracted paralysis=loosens its hold on the host.
not ovicidal only for adults. MAX CONC is crucial, not exposure

32
Q

What are the immunological effects of levamisole?

A

Restores depleted T cells back to their original number, wont increase them beyond this though.

33
Q

What is the spectrum of activity of Imidazothiazoles?

A

Broad spectrum anthelmintic- GI nematodes, lung worm, NOT tape worm or fluke.
For sheep and cattle
2-LV

34
Q

What are the adverse effects of Imidazothiazoles?

A

Relatively toxic due to activity at nicotinic receptors (AChEI), can have muscarinic stimulation. Would see PNS signs e.g. salivation, tremor, urination, defecation and collapse (bradycardia).
ATROPINE. Dog and horse are more susceptible.

35
Q

What are the three examples of Tetrahydropyrimidines?

A

Morantel, Oxantel, Pyrantel.

36
Q

What is pyrantel derived from and what does it do?

A

An imidazothiazole.

Reduces GI absorption=inc contact time, food delays absorption.

37
Q

What is the spectrum of Pyrantel and how is it administered?

A

GI nematode used in dogs, cats and horses (compound wormer), Administered orally in a paste or tablet.

38
Q

Which tetrahydropyrimidine is used in food producing animals?

A

Morantel- greater efficacy than pyrantel.
Suspension in sheep or ruminal bolus for cattle.
GI nematodes- undergoes FPE.
2-LV

39
Q

What are the characteristics of Monepantal?

A

New drug- Amino acetonitrile derivative, 4-AD (orange).
Targets the nicotinic ACh receptor.
7- day meat withdrawal (short)
GI nematodes- no current resistance, only for sheep e.g. haemonchus

40
Q

What is abamectin/derquantel for?

A

purple, 5 SI, nicotinic ACh antagonist for sheep.
60% bioavailability (F), hepatic metabolism, excretion in faeces.
Adult and immature GI nematodes, adult lung worm.

41
Q

What are salicylanilides and what is their mechanism of action?

A

They are flukicides. e.g. closantel and oxyclozanide.

They uncouple oxidative phosphorylation in the parasite by increasing mitochondrial permeability.

42
Q

What are salicylanilides effective against and what is its range in efficacy?

A

fasciola hepatica and haemonchus contortus in sheep and cattle.
8wk- adult fluke >92%
6wk 70%

43
Q

what are the characteristics of Nitronxynil?

A

It is a flukicide- Substituted phenol that uncouples oxidative phosphorylation and is given parenterally. It has high PPB, long t1/2, given s/c in sheep and cattle.
STAINS WOOL

44
Q

What are the characteristics of Clorsulon?

A

It is a flukicide- sulphonamine.

It inhibits glycolytic pathways and can be administered orally or parenterally. Effective against 8wk + fluke.

45
Q

What is Praziquantel and how does it work?

A

Effective against tapeworm (all spp and stages) It causes Ca influx into the parasite and induces tetanic contraction.

46
Q

How is praziquantel metabolised and excreted?

A

By the liver especially if given orally and it is rapidly absorbed by the GI tract and well distributed.

47
Q

What are the cyclo-depsipeptides?

A

New class, the only licensed one is emodepside.

48
Q

What is the mechanism of action of emodepside?

A

(not fully clear)
Drug binds to iatrophillin receptor which is a GPCR that stimulates PLC.= flaccid paralysis of the parasite-pharyngeal mm.

49
Q

What is the spectrum of activity of Emodepside?

A

Broad spectrum, only for use in the cat- toxocara cati.

50
Q

What are the pharmacokinetics of Emodepside when in combo with praziquantel?

A

spot-on, t1/2 9 days, fat acts as a reservoir so it is distributed from here, relatively safe.

51
Q

What nematode wormer is used on puppies and kittens?

A

Piperazine

52
Q

What are arsenicals and what do they do?

A

They are used for the treatment of heartworm, they have a narrow therapeutic index.
Trivalent arsenic binds to sulfhydryl groups on proteins which alters their function- mitochondrial enzymes esp.

53
Q

What is Melarsomine hydrochloride and how is it used?

A

An arsenical- Dirofilaria immitis, deep i/m, 2 injections 24hrs apart, t1/2=3h.

54
Q

What are the adverse effects of melarsomine hydrochloride?

A

Indirect pulmonary thromboembolism

Pain and swelling at the injection site (prescribed NSAIDS)

55
Q

How can Benzimidazole resistance be identified?

A

By PCR which is much more precise than FEC.

56
Q

What are the 4 methods of preventing resistance?

A

1) rotational use of anthelmintics
2) Use of correct dose and regime
3) use of combinations of anthelminitic with different mechanisms of action
4) use of management to reduce need of anthelmintic use
(pasture management no longer recommended.

Applied Pharmacology (5 decks)

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