Antiparasitics

Question 1

Ectoparasitics

Answer 1

Treat Ectoparasites

Question 2

Anthelmintics

Answer 2

Treat worm infections

Question 3

Antiprotozoals

Answer 3

treat protozoan parasite infections

Question 4

Endectocides

Answer 4

treat internal parasitic infections and

external parasitic infestations

Question 5

2 groups of Helminths

Answer 5

Nematodes, Platyhelminthes

Question 6

Platyhelminthes

Answer 6

flattened 
worms that are subdivided 
into two groups:
 Cestodes (tapeworms)
 Trematodes (flukes)

Question 7

Nematodes

Answer 7

cylindrical,
nonsegmented worms
commonly called
roundworms

Question 8

Anti nematodals (6 groups)

Answer 8

Benzimidazole drugs
Imidazothiazoles
Tetrahydropyrimidines
Organophosphates
Piperazine compounds
Macrocyclic lactones (Avermectins)

Question 9

Benzimidazoles (facts)

Answer 9

 Work by interfering with energy metabolism of the worm
 Recognize by –azole ending in drug name
 Always read the label to determine which parasites a drug
is effective against
 All can be administered orally, either as a paste, a
granulated powder, or a solution.
 Side effects are rare with benzimidaloles, but may include
vomiting, diarrhea, and lethargy

Question 10

Benzimidazoles (Groups)

Answer 10

Droncit plus (fenbantel) also contains praziquantel/pyrantel pamoate
Tresaderm (thiabendazole)
Anthelcide EQ Equine Wormer Paste (oxibendazole)
Telmintic (mebendazole) -
Panacur (fenbendazole)
Valbazen (albendazole)

Question 11

Thiabendazole (facts)

Answer 11

 Effective against strongyles and ascarids
 Also has antifungal and anti-inflammatory effects
 Suitable for otic preparations such as Tresaderm®
 Tresaderm® also contains dexamethasone and neomycin
sulfate
 Dexamethasone is a synthetic adrenocorticoid steroid
that inhibits the reaction of connective tissue to injury
and suppresses the classic inflammatory manifestations
of skin disease.
 Neomycin is a broad-spectrum aminoglycoside

Question 12

Anticoccidials

Answer 12

 Coccidiosis is a protozoal infection that causes intestinal
disorders
 Most anticoccidial drugs are coccidiostats (do not actually
kill the parasite, so hygiene is crucial)
 Sulfadimethoxine (Albon®)
 Reduces the number of oocysts shed, thus reducing spread of
disease
 Ponazuril (Marquis®)
 Equine antiprotozoal oral paste ; used off-label in dogs/cats
 Kills coccidia
 Given in 3 doses – days 1, 2, and 9.
 30 mg/kg of a 50 mg/mL solution
 Others (work mainly by affecting the protozoan’s
metabolism)
 Nicarbazine, Amprolium, Monensin, Decoquinate, Robenidine

Question 13

Antiprotozoals

Answer 13

 Giardiosis is a protozoal disease caused by Giardia
spp.
 Antiprotozoal drugs
 Metronidazole (Flagyl®) (enters the protozoal cell and
interferes with its ability to function and replicate)
 Fenbendazole (Panacur®)
 Albendazole (Valbazen®)
 Giardia Vaccine (GiardiaVax®)
 Blood protozoan Babesia sp. is transmitted by ticks
 Imidocarb (injectable) has cholinergic effects on the
protozoan
 Tick prevention also important

Question 14

Oxibendazole

Answer 14

 Used as a horse dewormer and in combination products for dogs.
 Can cause liver toxicity in dogs
 Anthelcide EQ Equine Wormer Paste ®

Question 15

Mebendazole

Answer 15

 A granular powder used in dogs and horses to treat ascarid,
hookworm, and cestode infections.
 Severe liver toxicity has been reported
 Also used in humans for roundworms, pinworms, tapeworms,
and hookworms
 Telmintic®
 Approved for use in dogs; not cats; not dewormer of choice; safer
alternatives are available

Question 16

Fenbendazole

Answer 16

 Wide spectrum of activity (roundworms,
hookworms, whipworms, and Taenia
pisiformis)
 Must be given for 3 consecutive days
 Also used to treat metronidazole-resistant
giardiasis.
 Side effects include vomiting and diarrhea
 Not approved for use in lactating dairy
animals
 Panacur® - available in granules,
suspensions, and pastes.

Question 17

Imidazothiazoles

Answer 17

 Work by stimulating the nematode’s cholinergic
nervous system, leading to paralysis of the
parasite (therefore, not ovicidal)
 Effective against ascarids, strongyles, whipworms,
and hookworms
 Was used as a microfilaricide in the past
 An example is levamisole (Levasol®)
 Expels most nematodes in 24 hours (some may be
passed alive)
 Available in oral forms such as pellets, powder,
suspensions, and pastes
 Also has anti-inflammatory and immunostimulant
properties
 May cause toxicity in host animal due to
cholinergic effects

Question 18

Tetrahydropyrimidines

Answer 18

 Mimic the action of ACh and cause 
initial stimulation then paralysis of 
the worm
 Effective against ascarids, pinworms, 
strongyles, and hookworms
 Examples include pyrantel
pamoate, pyrantel tartrate, and 
morantel tartrate
 Taste = somewhat pleasant
 Very safe.
 Nemex®, Strongid-T®

Question 19

Organophosphates

Answer 19

 Inhibit cholinesterase activity, causing
ACh to remain active in the
neuromuscular junction of the parasite
 Are neurotoxic to parasites; some cause
neurologic side effects in the host
 Both endoparasitic and ectoparasitic
 Narrow range of safety; not for use in
heartworm-positive dogs
 Effective against bots and a variety of
nematodes
 Dichlorvos (Task®)
 Not safe to use OPs off-label!!!

Question 20

Organophosphates (side effects)

Answer 20

 Salivation
 Lacrimation
 Urination
 Dyspnea
 Defecation
 Emesis
 Also ataxia, anxiety, abdominal pain, muscle 
twitching, pupillary constriction, seizures…

Question 21

Piperazine

Answer 21

 Blocks neuromuscular 
transmission in the parasite
 Effective only against ascarids
 Clients should be made aware 
that piperazines often result in 
intact worms being vomited or 
passed in stool.
 Practically nontoxic
 Sold OTC
 Hartz Health Measures Once-a-Month 
Wormer® for Puppies
 Pipa-Tabs®

Question 22

Macrocyclic Lactones

Answer 22

 Avermectins (macrocyclic lactones)
 Bind to certain chloride channels in the parasite nerve and
muscle cells, causing paralysis and death of the parasite
 The representative of this group is ivermectin, used for a
wide variety of endo- and ectoparasites
 May be combined with other antiparasitic agents to broaden its
spectrum of activity
 Heartgard Plus® (contains ivermectin and pyrantel pamoate)
 Oral (Heartgard®) and parenteral forms (Ivomec®) available
 Used for heartworm prevention
 Collies are ivermectin sensitive
 Another example in this group is moxidectin (ProHeart-6®,
Advantage Multi®)
 Not effective against cestodes or trematodes

Question 23

Anticestodals (3 groups)

Answer 23

Praziquantel, Epsiprantel,Fenbendazole

Question 24

 Epsiprantel

Answer 24

 Effective against Taenia spp. and Dipylidium caninum, but not
Echinococcus spp.
 Like praziquantel, disintegrates cestode so that it can be digested
by host
 Unlike praziquantel, not absorbed well by GI tract, so systemic side
effects are minimal.
-Cestex

Question 25

Praziquantel

Answer 25

 Works by increasing the cell membrane
permeability of the cestode, thus reducing its
resistance to digestion in the host’s intestinal
tract. Ultimately, after administration of
praziquantel, the entire tapeworm
disintegrates (including the scolex).
 Owners will not see tapeworm or segments
passed after treatment
 Works on all cestode species
 With Dipylidium caninum, it is especially
important to also eradicate fleas to prevent
reinfection.
 Available as oral tablet or injectable
 Side effects are rare; include anorexia,
vomiting, diarrhea, and lethargy

Question 26

Fenbendazole (Anticestodal)

Answer 26

 A benzimidazole (covered previously – antinematodals)
 Effective against Taenia spp. but not Dipylidium caninum
 Unless other parasites are present in animal that can be treated with
fenbendazole, praziquantel or epsiprantel are recommended.

Question 27

Antitrematodals (Groups)

Answer 27

Clorsulon, Albendazole, Praziquantel

Question 28

Praziquantel (Antitrematodals)

Answer 28

 Covered previously (anticestodal)

 Also effective against lung flukes in dogs and cats

Question 29

Albendazole

Answer 29

 Benzimidazole that interferes with the energy
metabolism of the worm
 Also effective against some nematodes (broadspectrum)
 Not approved for use in lactating animals

Question 30

Clorsulon

Answer 30

 A benzene sulfonamide
 Works by inhibiting the trematode’s enzyme systems for 
energy production (robs fluke of energy)
 Effective against Fasciola hepatica
 Adult and immature forms
 OTC
 Drench
 Not recommended in dairy animals