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Undeleted > Anthelmintics > Flashcards

Anthelmintics Flashcards

1
Q

What is the mechanism of action of benzimidazoles?

A
  • bind to tubulin and inhibit microtubule formation
  • inhibition of mitochondrial furmate reductiase
  • reduced glucose transport
  • uncoupling of oxidative phosphorylation
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2
Q

What are the pharmacokinetics of benzimidazoles

A
  • very poor water solubility
  • limited absorption from GIT (<1% of oral dose in plasma)
  • efficiacy is improved with an increased gut transit time (give with food)
  • metabolism is variable:
    reduction: sulphoxide—-sulphide
    oxidation: sulphide—sulphoxide—sulphone
    cyclization: netobimin—albendazole
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3
Q

Do benzimidazoles have any side effects?

A

no

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4
Q

Do benzimidazoles have any contraindications?

A

teratogenic

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5
Q

What is the spectrum of benzimidazoles?

A

broad: larvacidal and ovicidal

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6
Q

What is the chemistry of imidazothiazoles?

A
  • tetramisole-racemix mixture
  • levamisole is the L-isomer of DL-tetramisole
  • highly water soluble
  • marketed as hydrochloride or phosphate
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7
Q

What is the mechanism of action of imidazothiazoles?

A

-binds to and stimulates nictoinic receptors resulting in paralysis of the nematode by sustained muscle contraction. Parasite can’t hold onto GIT and is passed in faeces.

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8
Q

What are the pharmacokinetics of imidazothiazoles?

A
  • highly water soluble

- absorbed and excreted rapidly (<1% in tissues after 24hrs)

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9
Q

Do imidazothiazoles have any contraindications?

A

respect withdrawal periods

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10
Q

What is the spectrum of imidazothiazoles?

A

adult and larval GI roundworms and lungworms

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11
Q

What is the chemistry of tetrahydropyrimidines?

A
  • pyrantel is an imidazothiazole derivative prepared as the tartate or pamoate salt.
  • morantel is a methyl-substituted analogue of pyrantel
  • stable as solid but solutions are photosensitive
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12
Q

What is the mechanism of action of tetrahydropyrimidines?

A

depolarising neuromuscular blocking agents which paralyse worms

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13
Q

What are the pharmacokinetics of tetrahydropyrimidines?

A
  • not well absorbed by GIT
  • quickly metabolised
  • 25-40% excreted in urine, rest in faeces
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14
Q

Do tetrahydropyrimidines have any side effects?

A

no

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15
Q

Are there any contraindications of tetrahydropyrimidines?

A
  • not for use in severely debilitated animals

- observe withdrawal period

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16
Q

What is the spectrum of tetrahydropyrimidines?

A

adult GI nematodes

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17
Q

What is the chemistry of organophosphates?

A
  • DDVP is incorporated into polyvinylchloride pellets

- 50% is released before excretion

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18
Q

What is the mechanism of action of organophosphates?

A

inhibition of acetylcholinesterase (AchE) which causes Ach to build up in synaptic cleft and nematode becomes paralysed

doesn’t affect host as mammalian AchE has much lower affinity for organophosphates.

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19
Q

Are there any side effects of organophosphates?

A

YES

  • signs of toxicity include twitching, salvation etc (muscurinic and nicotinic effects)
  • drug can build up over time
  • observe withdrawal period
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20
Q

Are there any contraindications of organophosphates?

A

YES
not for use with AchE inhibitors, muscle relaxants, carbamate
not for use in lactating animals

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21
Q

What is the spectrum of organophosphates?

A

principle parasites of horses, dogs and pigs

not so good in ruminants

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22
Q

What is the chemistry of macrocyclic lactones?

A
  • large molecules with a complex structure

- very lipid soluble

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23
Q

What is the mechanism of action of macrocyclic lactones?

A

stimulate glutamate-gated chloride channels in invertebrate muscle and nerve cells. This allows a large to influx of Cl into cell causing hyperexcitibility and hyperpolarisation of post synaptic cell.
This interferes with neurotransmission and results in flaccid paralysis.

24
Q

Are there any side effects of macrocyclic lactones?

A

No

-lipophillic so cross BBB

25
Q

What are the pharmacokinetics of Invermectin?

A
  • semi-synthetic derivative of avermectin.
  • stable at room temperature in non-acidic contiions
  • very lipid soluble
  • very photosensitive
  • half life depends on admin (IV=2days, SC=8days)
  • oral admin decreases bioavailability
  • residues up to 14 days
  • 1st pass metabolism
  • 98% faecal excretion
26
Q

What is the spectrum of Invermectin?

A
  • all major GI and lung nematodes of cattle, sheep, horses and swine
  • GI nematodes and heartworms of dogs
27
Q

What is the chemistry and spectrum of Albamectin?

A
  • avermectin B1a (80%) and B1b (20%)

- nematode and arthropod parasites of cattle

28
Q

What is the chemistry of doramectin?

A

-substitutes cyclohexyl invermectin

29
Q

What are the pharmacokinetics of doramectin?

A
  • twice halflihofe of invermectin
  • twice plasma concentration of invermectin
  • lipid based carrier
30
Q

What is the spectrum of doramectin?

A
  • persists for 12 days against cooperia

- persists for 21 days against ostertagia

31
Q

What is the pharmacokinetics of eprinomectin?

A
  • very rapidly and readily absorbed through the skin
  • peak plasma concentration at 2-5 days
  • 85% excreted unchanged
32
Q

What is the spectrum of eprinomectin?

A

99% of bovine GI nematodes

33
Q

What are the pharmacokinetics of selmectin?

A
  • absorbed rapidly after admin

- half life is 11 days

34
Q

What is the spectrum of selamectin?

A

nearly all cat and dog parasites

35
Q

What is the pharmacokinetics of milbemycin oxime?

A

90-95% remains in GIT

36
Q

What is the spectrum of milbemycin oxime?

A

endectocides

37
Q

Does milbemycin oxime have any side effects?

A

YES: transient trembling/ataxia

38
Q

What are the pharmacokinetics of moxidectin?

A

more lipophillic than invermectin

39
Q

what is the spectrum of moxidectin?

A

endectocides

40
Q

Does moxidectin have any side effects?

A

No

41
Q

What is the mechanism of action of heterocyclic compounds?

A

Piperazine: hyperpolarisation of muscle membranes at he neuromuscualr junctions causes flaccid paralysis.
Also GABA agonist
DEC: opsonizes larval (L3/L4) heartworms

42
Q

What are the pharmacokinetics of heterocyclic compounds?

A
  • readily absorbed from GIT
  • Piperazine: 30-40% excreted unchanged
  • DEC: 10-25% excreted unchanged
43
Q

What is the spectrum of heterocyclic compounds?

A

Piperazine: ascarids and nodular worms
DEC: canine heartworm

44
Q

Do heterocyclic compounds have any side effects?

A

No

45
Q

Do heterocyclic compounds have any contraindications?

A

Piperazine: long standing liver/renal disease
DEC: microfilaria

46
Q

What is the mechanism of action of cycloctadepsipeptides?

A

Inhibition of Ach-elicitated muscle contractions as it decreases the amount of Ach released pre-synaptically in response to a stimulus.
Results in flaccid paralysis

47
Q

What are the pharmacokinetics of cycloooctadepsipeptides?

A
  • extensively distributed
  • high volume distribution
  • minor metabolism
  • excreted unchanged in bile
48
Q

What is the spectrum of cyclooctadepsipeptides?

A
  • high efficacy against adult nematodes.
  • variable efficacy against larvae
  • combined preperation against tapeworms, hookworms and roundworms.
49
Q

What are the pharmacokinetics of praziquantel?

A
  • soluble in organic solvents
  • rapidly absorbed and widely distributed
  • 70% first pass metabolism
  • 80% eliminated within 24 hours
50
Q

What are anticestidals?

A
  • praziquantel
  • benzimidazoles
  • pyrantel
  • dichlophen and nitroscanate
  • bunamidine
  • niclosamide
51
Q

What are antitrematodals?

A
  • benzimidazoles
  • salicylanides
  • nitroxynil
  • clorsulan
  • diamphenethide
52
Q

What is the mechanism of action of salicylanides?

A
  • proton ionophore

- uncouples oxidative phosphorylation

53
Q

What are the pharmacokinetics of Rafoxanide?

A
  • salicylanide
  • rapidly absorbed
  • not metabolised
  • highly protein bound
  • half life is 16.6 days
54
Q

What are the pharmacokinetics of Closantel?

A
  • salicylanide
  • highly plasma protein bound
  • half life= 14.5 days
55
Q

What is the mechanism of action and half life of Nitoxymil?

A
  • uncouples oxidative phosphorylation

- long half life

56
Q

What is the mechanism and half life of Closulan?

A
  • inhibits 3-phosphoglycerate kinase and phosphoglycero-mutase
  • short half life
57
Q

What is the mechanism of action of Diamphenethide

A

deacylated to active metabolites in liver parenchyma causes change in the parasite integument
-wide distribution

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