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MODULE 16 - Alimentary Tract Disease > PHARMACOLOGY - Anthelmintics > Flashcards

PHARMACOLOGY - Anthelmintics Flashcards

1
Q

What are the three anthelmintic treatment strategies?

A

Interval treatment
Targeted treatment
Stategic treatment

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2
Q

What is interval anthelmintic treatment?

A

Interval anthelmintic treatment involves administering anthelmintics at specific time intervals to maximise impact based on the knowledge of the lifecycle of the parasite and the peristence of the drug

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3
Q

What is targeted anthelmintic treatment?

A

Targeted anthelmintic treatment involves administering anthelmintic drugs based on confirmed diagnosis of the parasite

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4
Q

What is strategic anthelmintic treatment?

A

Strategic anthelmintic treatment involves administering anthelmintic drugs based on confirmed diagnosis of the parasite, as well as considering the parasite lifecycle, seasonality, and risk of transmission

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5
Q

What are the main routes of administration used for canine anthelmintic products?

A

Oral
Spot-on

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6
Q

What are the main routes of administration used for feline anthelmintic products?

A

Oral
Spot-on

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7
Q

What are the possible legal classifications of canine and feline anthelmintic products?

A
  1. Prescription-only Medicines - Veterinarian (POM-V) (most common)
  2. Non-Food Animal Medicines - Veterinarian, Pharmacist, Sutiable Qualified person (NFA-VPS)
  3. Authorised Veterinary Medicines - General Sales List (AVM-GSL)

The AVM-GSL usually aren’t very affective

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8
Q

What are the main routes of administration used for equine anthelmintic products?

A

Oral

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9
Q

What is the legal classification of equine anthelmintic products?

A

Non-Food Animal Medicines - Veterinarian, Pharmacist, Sutiable Qualified person (NFA-VPS)

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10
Q

What are the main anthelmintic drug classifications?

A

Benzimidazoles
Macrocyclic lactones
Tetrahydropyramidines
Praziquantel
Emodepside

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11
Q

What is the mechanism of action for benzimidazoles?

A

Benzimidazoles bind to helminth tubulin, preventing microtubule formation which prevents mitotic spindle formation as well as glucose uptake which result in starvation of the helminth

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12
Q

Describe the nature of selective toxicity of benzimidazoles

A

Benzimidazoles have a high affinity and irreversible binding to helminth tubulin, however they have low affinity and reversible binding to mammalian tubulin

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13
Q

Which parasites are targeted by benzimidazoles?

A

Nematodes
Cestodes
Trematodes

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14
Q

What is the route of administration for benzimidazoles?

A

Oral

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15
Q

Why can benzimidazoles only be administered orally?

A

Benzimidazoles have a limited solubility and thus form a suspension - described as a white drench - which can only be administered orally as it is not sufficiently dissolved to be administered via other routes

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16
Q

(T/F) Benzimidazoles are well absorbed into the plasma

A

FALSE. Benzimidazoles have limited absorption from the gastrointestinal tract into the plasma which is beneficial as this allows the drug to target the gastrointestinal parasites

Limited GI absorption means that it will not be as effective against larval stages

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17
Q

What can be done to increase the efficacy of benzimidazoles?

A

Slowing gut transit time by administering benzimidazoles with food increases the efficacy

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18
Q

What happens when benzimidazoles are absorbed into the plasma?

A

Benzimidalozes are very rapidly cleared from the plasma

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19
Q

How are benzimidazoles metabolised?

A

Benzimidazoles are metabolised by redox reactions - reactions where reduction and oxidation are both taking place

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20
Q

Which benzimidazole metabolites are produced via the reduction pathway?

A

Reduction reactions produce sulphoxides which can be further reduced into sulphides

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21
Q

Which benzimidazole metabolites are produced via the oxidation pathway?

A

Oxidation reactions produce sulphides which can be further oxidised into sulphoxides which can be further oxidised into sulphones

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22
Q

Which benzimidazole metabolites are active?

A

Sulphides
Sulphoxides

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23
Q

Which benzimidazole metabolite is inactive?

A

Sulphones

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24
Q

How are benzimidazoles primarily excreted?

A

Benzimidazoles are primarily excreted faecally

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25
Q

What are the contraindications to the use of benzomidazoles?

A

Benzimidazoles are teratogenic and thus are contraindicated in early pregnancy

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26
Q

Give two examples of benzimidazoles liscenced for use in companion animals in the UK

A

Fenbendazole
Menbendazole

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27
Q

What is the mechanism of action for macrocyclic lactones?

A

Macrocyclic lactones stimulate glutamate gates chloride channels in invertebrate nerve and muscle cells resulting in an influx of chloride and persistent hyperpolarisation, resulting in flaccid paralysis. There is also evidence that macrocyclic lactones can target GABA receptors

28
Q

Describe the nature of selective toxicity of macrocyclic lactones

A

Macrocyclic lactones target glutamate-gated chloride channels which don’t exist in mammals

29
Q

Which parasites are targeted by macrocyclic lactones?

A

Macrocyclic lactones are endectocides meaning they target both nematodes and ectoparasites

30
Q

What are the possible routes of administration for macrocyclic lactones?

A

Subcutaenous
Oral
Topical (i.e. Spot-on)

31
Q

Describe the pharmacokinetics of macrocyclic lactones

A

Macrocyclic lactones are well absorbed particularly when administered subcuteneously or orally - topical administration is more variable. Regardeless of the route of administration, due to their lipid solubility macrocyclic lactones have a high volume of distribution (Vd) and accumulate in adipose tissue

High Vd means that it will be effective against larval stages

32
Q

Why does topical/spot-on administration of macrocyclic lactones have a longer half life than other routes of administration?

A

When macrocyclic lactones are administered topically/spot-on, they are absorbed into the subcutaenous fat where is accumulates and creates a reservoir, resulting in a longer half-life

33
Q

How are macrocyclic lactones metabolised?

A

Macrocyclic lactones have very minimal metabolism and are mostly excreted unchanged

34
Q

How are macrocyclic lactones excreted?

A

Macrocyclic lactones are mostly excreted unchanged in the faeces and small amounts are excreted in the urine

35
Q

What contributes to the long plasma half life of macrocyclic lactones?

A

The high volume of distribution and slow excretion of macrocyclic lactones contributes to their long plasma half life

36
Q

Give three examples of macrocyclic lactones

A

Ivermectin
Selamectin
Milbemycin oxime

37
Q

Why is ivermectin no longer liscenced in small animals?

A

Lipophilic drugs can cross the blood brain barrier however they are pumped back out by p-glycoproteins. However, there are certain breeds (such as herding dogs) that have a genetic mutation in the ABCB1 gene which affects these p-glycoprotein, allowing the drug to accumulate in the brain. Though mammals do not have glutamate gated chloride channels, they do have GABA receptors which can be affected by ivermectin resulting in side effects

38
Q

(T/F) Ivermectin is liscenced for use in horses in the UK

A

TRUE.

39
Q

Which species’ is selamectin liscenced in?

A

Dogs
Cats

40
Q

Why can selamectin be used safely in dogs and cats?

A

Selamectin is safe in breeds with ABCB1 gene mutations as it does not require p-glycoproteins to be removed from the blood brain barrier

41
Q

What is the route of administration for selamectin?

A

Topical (Spot-on)

42
Q

Which species’ is milbemycin oxime liscenced in?

A

Dogs
Cats

43
Q

What is the route of administration for milbemyxin oxime?

A

Oral chewable tablets

44
Q

Which pharmacokinetic property should be you be aware of when administering milbemyxin oxime?

A

Despite milbemyxin oximes high lipid solubility, it isn’t well absorbed from the gastrointestinal tract to is more for targeting gastrointestinal parasites

Limited GI absorption means that it will not be as effective against larval stages

45
Q

What are the potential side effects of milbemyxin oxime?

A

Transient trembling and ataxia

This tends to only occur due to overdose

46
Q

What is the mechanism of action of tetrahydropyramidines?

A

Tetrahydropyramidines stimulate the nicotinic acetylcholine receptors at the neuromuscular junction, resulting in persistent depolarisation and spastic paralysis

47
Q

Describe the nature of selective toxicity of tetrahydropyramidines

A

Tetrahydropyramidines have a higher affinity for helminth nicotinic acetylcholine receptors than mammalian nicotinic acetylcholine receptors

48
Q

What is the most significant example of a tetrahydropyramidine?

A

Pyrantel

49
Q

Which species’ is pyrantel liscenced in?

A

Dogs
Cats
Horses

50
Q

Which parasites are targeted by pyrantel?

A

Nematodes
Cestodes (in some equine products)

51
Q

Which pharmacokinetic property should be you be aware of when administering pyrantel?

A

Despite the high lipid solubility of pyrantel, it is not well absorbed from the gastrointestinal tract and thus is used to target gastrointestinal parasites

Limited GI absorption means that it will not be as effective against larval stages

52
Q

What can be done to increase the efficacy of pyrantel?

A

Slowing gut transit time by administering pyrantel with food increases the efficacy

53
Q

How is pyrantel metabolised?

A

Approximately 50% of pyrantel is metabolised and the rest is excreted unchanged

54
Q

What is the primary route of excretion of pyrantel?

A

Pyrental is primarily excreted in the faeces

55
Q

What is the mechanism of action of praziquantel?

A

Praziquantel causes a rapid influx of calcium into the helminth resulting is tetanic contraction of the musculature as well as causes a ionic disturbance which draws water into the helminth resulting is vacuolisation of the syncytial tegument, allowing the host immune system to clear the helminth

56
Q

Which parasites are targeted by praziquantel?

A

Cestodes (mainly)
Trematodes

57
Q

What is the main route of administration for praziquantel?

A

Oral

58
Q

Describe the pharmacokinetics of praziquantel

A

Praziquantel is rapidly absorbed and has a high volume of distribution due to its high lipid solubility

High Vd means that it will be effective against larval stages

59
Q

Why does praziquantel have such a short duration or action?

A

Praziquantel has such a short duration of action as it undergoes first pass metabolsim and rapid elimination

60
Q

What is the mechanism of action for emodepside?

A

Emodepside inhibits acetylcholine elicited muscle contraction through binding to latrophilin-like receptors at the neuromuscular junction, resulting in flaccid paralysis

61
Q

What is the nature of selective toxicity for emodepside?

A

Latrophilin-like receptors are not present in mammalian species

62
Q

Which species is emodepside liscenced in?

A

Cats

63
Q

Which parasites are targeted by emodepside?

A

Nematodes

64
Q

Describe the pharmacokinetics of emodepside?

A

Emodepside is rapidly absorbed and has a high lipid solubility resulting in a high volume of distribution (Vd). Emodepside is minimally metabolised and is rapidly excreted mostly unchanged in the bile

High Vd means that it will be effective against larval stages

65
Q

What is profender?

A

Profender is a commercially available combination of emodepside and praziquantel

MODULE 16 - Alimentary Tract Disease (7 decks)

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