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Parasitology > Anthelmentics > Flashcards

Anthelmentics Flashcards

1
Q

what is an anthelmentic and what are the two most important features of one

A

drug used to control parasites

  • spectrum of activity
  • safety index (ratio of toxic dose to therapeutic dose)
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2
Q

what class of drugs inhibit polymerization of tubulin formation in nematodes

A

benzimidazoles

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3
Q

what is a primary benzimidazole

A

thiabendazole (TBZ)

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4
Q

what are the 3 secondary benzimidazoles

A

cambendazole
parbendazole
oxibendazole

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5
Q

what are 3 tertiary benzimidazoles

A

Fenbendazole (FBZ)
albendazole (ABZ)
Oxfendazole (OFZ)

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6
Q

what can thiabendazole (TBZ) be used to treat

A 
broad spectrum (all gastro intestinal nematodes)
will kill migrating S vulgaris at 10X dosing rate
5 daily doses kills inhibited larvae of Ostertagia
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7
Q

what is the safety margin of TBZ

A

very high safety margin of above 10

non toxic

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8
Q

what are tertiary benzimidazoles used to treat

A

highly effective against inhibited ostertagia

currently in extensive use

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9
Q

what are some pharmacological features of the benzimidazoles

A

oral administration only- white drench
goes into rumen some gets to gut (depot effect)
metabolized to sulphoxidein liver->sulphone (anthelmentic activity)
OVICIDAL

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10
Q

what is the depot effect

A

metabolites of drugs also have anthelmentic effect

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11
Q

what species is benzimidazoles administered to and how

A

ruminants- drench
horses- paste
dogs, cats- tablets
pigs, poultry- powder

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12
Q

what is benzimidazole used to treat in ruminants

resistance?

A

tertiary
kills trichostrongyles and lungworms
kill inhibited and migrating larvae
widespread resistance in trichostrongyles in sheep

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13
Q

what is benzimidazole used to treat in horses

A

kill adult stages of all strongyles; kill migrating S. vulgaris larvae
NOT effective against inhibited cyathostomes (except when 5 daily doses used)
widespread resistance in cyathostomes

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14
Q

treatment with benzimidazole in dogs, cats, and pigs

A

no “depot”, must give 3-5 daily doses; mebendazole

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15
Q

what is imidazothiazoles- levamisole mode of action

A

cholinergic agonists at synaptic and extrasynaptic nicotinic acetylcholine receptors (motor end plates)
• depolarisation causes spastic paralysis
acting on the Nervous system

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16
Q

what does imidazothiazoles have activity against (worms)

A

nematodes including lung worms
not active against cestodes or trematodes
not active against inhibited larvae
Broad spectrum

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17
Q

how can imidazothiazoles be administered and what color is the drench

A

orally or parenterally, pour on (percutaneous absorbtion), intraruminally
clear drench

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18
Q

how does imidazothiazole act within the body

A 
rapidly absorbed from gut in ruminants and monogastrics
peak blood levels in 30 mins
excreted in urine in 6 hours
NOT ovicidal 
high safety index (easy to overdose)
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19
Q

is there resistance associated with imidazothiazole

A

widespread resistance in trichostrongyles of sheep and goats

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20
Q

which species are imidazothiazoles not used in and why

A

horses- causes excitement

21
Q

Tetrahydropyrimidines - Morantel, Pyrantel mode of action

A
  • depolarise motor end plates in muscle

* same site of action as levamisole (motor end plates)

22
Q

Tetrahydropyrimidines - Morantel, Pyrantel activity

A
  • most GINs; NOT lungworms**

* NO effect on inhibited larvae**

23
Q

Tetrahydropyrimidines - Morantel, Pyrantel pharmacokinetics and safety index

A 
• soluble
• administered orally
• rapidly absorbed
• excreted in urine
not ovicidal
SI: 7x
24
Q

Tetrahydropyrimidines - Morantel, Pyrantel use in sheep

A

widely (?) used
resistance in trichostrongyles
cross resistance with levamisole
if resistant to morantel, still susceptible to levamisole

25
Q

Tetrahydropyrimidines - Morantel, Pyrantel in cattle

A 
morantel capsule (releases drug for 90 days) widely used in Europe
resistance in trichostrongyles
26
Q

Tetrahydropyrimidines - Morantel, Pyrantel use in horses

A

not effective against inhibited cyathostomes used as also effective against cestodes

27
Q

Tetrahydropyrimidines - Morantel, Pyrantel use in dogs and cats

A

pyrantel rather than morantel used removes hookworms

often used with oxantel to kill whipworms

28
Q

macrocyclic lactones mode of Action

A

GABA agonists- bind with high affinity to glutamate gated chloride channels
->flaccid paralysis

29
Q

macrocyclic lactones actviity

A

all gastrointestinal nematodes and arthropods
-not cestodes or trematodes
extremely potent- very low dose is needed

30
Q

macrocyclic lactones pharmacokinetics

and safety index

A 
oral, injectable, pour-on
absorbed rapidly
short half life after oral admin
half life of moxidectin is 28 days- long acting
SI: 20x (very good)
31
Q

what effects does administering ML orally have

A

high drug availability at site of parasite

improved therapeutic response

32
Q

effects of administering ML parenterally/sub cutaneous

A

high drug systemic availability

extended persistence of antiparasitic acctivity

33
Q

effects of administering ML as a pour on

A

large skin depot of the drug
erratic percutaneous absorption
oral ingestion
large interanimal variability

34
Q

what animals are MLs used in and against what

A

Sheep- widely used, limited resistance in trichostrongyles (cooperia and haemonchus)
cattle: kills inhibited ostertagia, resistance only to cooperia
horses: moxidectin kills up to 80%; resistance in cyathostomes
dogs, cats: oral (milbemycin) or topical (selamectin)- lung and hookworms

35
Q

what is the environmental effect of ML

A

persists in feces killing arthropods outside of host

36
Q

what is the mode of action of OP

A

inhibits acetylcholinesterase- spastic paralysis

37
Q

what is the activity of OP

A

highly effective against haemonchus

higher doses needed to kill trichostrongylus and ostertagia

38
Q

where is OP used

A

only in sheep

there is no resistance present- so use in combo where resistance is an issue

39
Q

what is the mode of action of piperazine

A

agonist of GABA receptors->flaccid paralysis

relies on peristaltic movement to remove worms

40
Q

what is the activity of piperazine

A

narrow spectrum- ascarids and nodule worms
given orally
low toxicity

41
Q

what animals is piperazine used in and against what

A

horses- removes adult strongyles, does not kill inhibited cyathostomes
dogs, cats: effective against hookworms
pigs: oesophagostomum spp.

42
Q

what is the mode of action of closantel

A

uncouples oxidative phosphorylation

43
Q

how is closantel given and how long does it persist

A

orally

in blood for 4-6 weeks

44
Q

what species is closantel used in and against what

A

sheep- haemonchus, resistance limited but spreading

dogs: against hookworms, but rarely used

45
Q

what is the mode of action of monepantel

A

nematode specific ACR 23 nicotinic acetylcholine receptor sub unit-> spastic paralysis

46
Q

derquantel mode of action and what is it used for

A

nicotinic agonist-> flaccid paralysis- does not kill nematodes
used in sheep against dictyocaulus

47
Q

what treatments can be used against encysted larvae of small strongyles of horses

A

Fenbendazole @ 10mg/kg/day for 5 days Moxidectin @ 0.4 mg/kg

48
Q

what should be the deworming regime for puppies

A
  • treatment every 2 weeks prior to weaning
  • treatment every 4 weeks after weaning
  • treatment every 3 months after 6 months of age
49
Q

what should be the deworming regime for pregnant bitches

A

• Fenbendazole @ 50 mg/kg/day from 3 weeks prepartum to 2-15 days postpartum

Parasitology (13 decks)

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