Pharm 2 - Antihelminthics 1

drraythe's version from 2015-11-21 19:07


Question Answer
Define Antihelminthic drugsDrugs used to kill &/or expel the parasitic helminths in the host animal
What are the 2 types of Antihelminthic drugs?(1) Vermifuges - expels the helminths
(2) Vermicides - kills the helminths
How is the selectivity of Antihelminthics? Exceptions?Usually very selective (safe), working on receptors/metabolic processes/accumulation exclusive to the parasite. BUT Organophosphorus Compounds & Levamisole DO have risk for tox since they can affect the Host's cells too
Most Antihelminthics can be used in all species, but Levamisole is for only?Ruminants & Swine
Most Antihelminthics can be used in all species, but Praziquantel is for only?Dogs, cats & horses
Most Antihelminthics can be used in all species, but Piperazine is for only?Monogastric species (NO RUMIS)
Most Antihelminthics can be used in all species, but Salicylanilides, Nitroxynil & Clorsulon are for only?Ruminants
How do nematodes develop resistance to Nematodicides?They develop resistance to the MOA!
How do you prevent the development of resistance against Nematodicides? (2)(1) ROTATE TYPE OF NEMATODICIDE (so the MOA keeps changing...dont change to something w/in the same group)
(2) Minimum frequency of Tx

Benzimidazoles (GI & LUNG NEMATODES)

Question Answer
Benzimidazoles have what spectrum of activity? What is their safety margin?BROAD spectrum, WIDE margin of safety
What are the 2 Subclasses of Benzimidazoles?(1) Benzimidazole Thiazoles
(2) Benzimidazole Carbamates
What drug(s) are in the Benzimidazole Thiazole subclass?Thiabendazole
What drugs are in the Benzimidazole Carbamates subclass?Albendazole/Netobimin
What are the drugs in the Pro-Benzimidazole (PRO DRUG) category? What are they converted into?Netobimin (converted to Albendazole)
Febantel (converted to Fenbendazole)
BZD (Benzimidazole) Carbamates (describe their activity & dose needed & why this is so)Possess greater Antihelminthic activity → EVEN LARVICIDAL!! Since stronger, need a lower dose. This strength is bc they have...
(1) Enhanced receptor binding in parasites
(2) ↓ metabolic inactivation in host animal
Which Benzimidazole subgroup (Carbamates or Thiazoles) has larvacidal activity?CARBAMATES
What is the MOA of Benzimidazole?BZD binds irreversibly to nematode β-tubulin, prevents dimerization w/ α-tubulin & polymerization of tubulinoligomers into microtubules I.E., INHIBIT MICROTUBULE FORMATION (this is also selective for nematode tubulin not host)
How does resistance develop against Benzimidazoles?Development of β-tubulin isotypes w/ lower affinity for BZDs
What is the absorption of Benzimidazoles like? What ↑ the bioavailability of BZDs?Absorption is LIMITED. Presence of food in stomach ↑ the bioavailability of drug (ex: Fenbendazole)
What is the plasma conc of Benzimidazoles like? Who has a higher systemic avail?BZD level in plasma is always <1% of the dose administered & RUMINANTS have higher systemic avail.
Metabolism of Benzimidazoles (general)Hepatic!
Metabolism of BZD Carbamates is special how?(Hepatic) They are converted into ACTIVE METABOLITES! 1st metabolized to Sulfoxides, which are active & extend effectiveness, before being metabolized again to Sulphones, which are inactive
(Albendazole to Albendazole sulfoxide)
(Fenbendazole to Fenbendazole sulfoxide)
The metabolism of Albendazole & Fenbendazole is more rapid in who?Cattle & goats
Which Benzimidazole has poor metabolism & excreted unchanged in feces?Mebendazole
Benzimidazole clinical efficacy depends on?Effective concentration at the site of action in the parasite
How safe are BZDs?Well tolerated (safe!)
What are the contraindications of BZDs? (Which BZDs have which effects on who?) (2)(1) Substituted BZDs are not indicated during early pregnancy
(2) Parbendazole produces teratogenic effects in pregnant ewes (2nd to 4th week of gestation)
How do you admin BZDs?ORAL!! (Paste or suspension/powder or granules) → Rumis can have gradual release boluses
Whats special about the Pro-Benzimidazoles?(Netobimin & Febantel) they have 2 active metabolites!!
Which Pro-BZD is used in Rumis & monogastrics, bc it can be converted via hepatic enzyme & ruminal microorganisms? Explain how it differs in activity btwn the 2 sp.Netobimin!
In RUMIS → Nematocidal & Fasciolicidal activity
In MONOGASTRICS → Nematocidal & Cestocidal activity
Netobimin metabolic path?Netobimin → Albendazole - (Hepatic oxidation) → Albendazole Sulfoxide
Who can have Febantel?Horses
Febantel metabolic path?Febantel → Fenbendazole - (Hepatic oxidation) → Fenbendazole sulfoxide
What is Vercom? Effective against?Combination of Febantel (nematodes) & Praziquantel (cestodes)
What is Drontal Plus? For who against what?25 mg Febantel, 5 mg Pyrantel Pamoate & 5 mg Praziquantel FOR DOGS!!
(Effective against canine Ascarids, Hookworms, Whipworms & Echinococcus sp)
How safe is Febantel?Wide margin of safety
Febantel is effective against?GI & lung parasites
Febantel contraindications?Vercom paste & Drontal Plus are contraindicated in pregnant dogs & cats (NO PREGGOS)
Can you use BZDs in birds?Yes, for lung nematodes


Question Answer
Levamisole is effective against what?GI & lung nematodes
Levamisole routes of admin?Oral
How is Levamisole formulated, based on route of admin?ORAL = Hydrochloride salt paste
INJECTABLE = Phosphate salt
MOA of Levamisole? (Basic)(2)(1) Depolarization neuromuscular blockade
(2) Acts as immunostimulator (cell mediated)
How does Levamisole work as a depolarization neuromuscular blockade?It acts as a ganglionic stimulant & a direct cholinergic drug → it binds to nicotinic receptors of nematodes → sustained mm contraction & subsequent paralysis
What is the speed of the absorption & excretion of Levamisole? What is its pharmacodynamic action?RAPID absorption & secretion. Pharmacodynamic action is of nicotinic & muscarinic effects
How can Levamisole be administered?Bolus
Drench (Topical pour-on)
Feed additive
SC injxn
What special action can Levamisole have, in who?In DOGS, can act as a Heartworm microfilaricide (along w/ being GI & LUNG nematodes)
How is the safety margin of Levamisole?NARROW (but leva is 4 times more safe than Tetramisole)
Tox of Levamisole in who?SHEEP! (Salivation, Lacrimation, Head shaking, Muscle tremors, Mild excitability)
What is the safe route of Levamisole for cats & dogs?Oral
What can make a Levamisole tox worse?Simultaneous administration of Pyrantel Tartrate or any Cholinesterase Inhibiting drugs
When is Levamisole contraindicated?DAIRY COWS (Excreted into milk & no established withdrawal time)
What is the big ol' WARNING about Levamisole for you?WEAR GLOVES! Leva can have percutaneous absorption (topical absorption) & cz agranulocytosis (LOW WBC count)

Tetrahydropyrimidines (NEMATODES)

Question Answer
Tetrahydropyrimidines are most effective against?GI nematodes
What 2 drugs do we care about in the Tetrahydropyrimidines?Pyrantel & Morantel
Pyrantel spectrum? For who?BROAD spectrum all species
What are the 2 forms Pyrantel is available in?Tartrate or Pamoate salt
What solution cz Pyrantel to lose potency?Aqueous solution undergoes photoisomerization → loss of potency
MOA of Pyrantel & Morantel?Depolarizing neuromuscular blocking agent in nematode parasites. Cz sustained muscle contraction followed by paralysis of worms. (MORE potent than Acetylcholine)
Pyrantel Tartrate → How is the absorption? Exceptions? Speed of metabolism? Excretion? Sp. diffs?WELL ABSORBED (except in ruminants), it is rapidly metabolized (does undergo 1st pass effect), & is excreted in Urine (DOGS) & Feces (RUMINANTS)
Pyrantel Pamoate → What worm does Pamoate work on, & how come it's so good at this?Poorly soluble in water → ↓ absorption from the gut → drug reaches the lower intestine & acts on pinworms (this is the 1 most clinics use)
Which 2 drugs have a more potent NM blockade effect than ACh? (Acetylcholine)Pyrantel & Morantel
What is in Drontal Plus for dogs?Pyrantel Pamoate(5 mg/kg) + Febantel(25 mg/kg) + Praziquantel(5mg/kg)
What is in Drontal for cats?Pyrantel Pamoate(20 mg/kg) + Praziquantel(5 mg/kg)
What is in Heartgard 30 Plus? For who? Effective against what?Contains Ivermectin(6-12 g/kg) + Pyrantel Pamoate(5-10 mg), for DOGS, effective against heartworms, hookworms & ascarids
Why would you want to give Pyrantel to a horse?Effective against Anaplocephala perfoliata tapeworm (ileocecal junction tapeworms)
Why would you want to give Pyrantel to a cattle/sheep?It is effective against BZD RESISTANT STRAINS of Haemonchus contortus (barber pole worm) (GI worm)
Safety of Pyrantel salts?Generally safe in all species EXCEPT FOR HORSES
Contraindications of Pyrantel salts? (2)(1) Not indicated in severely debilitated animals
(2) Withdrawal period for food animals needed
What is Morantel used for? (In who?) Anything to note about food animals?RUMNANTS! GI nematode adult & immature stages. Withdrawal period needed!!
Whats the route of admin she emphasized for Morantel?Sustained release ruminal bolus (Morantel slow release trilaminate bolus) ← Cylindrical tri-walled cartridge
Which is a safer drug - Pyrantel Tartrate or Morantel Tartrate?MORANTEL IS SAFER