Chemistry - A pyrimidine-derivative anthelmintic, pyrantel pamoate occurs as yellow to tan solid and is practically insoluble in water and alcohol. Pyrantel tartrate is more water soluble than is the pamoate salt. Each gram of pyrantel pamoate is approximately equivalent to 347 mg (34.7%) of the base. Pyrantel pamoate may also be known as pyrantel embonate .
Storage/Stability/Compatibility - Pyrantel pamoate products should be stored in tight, light-resistant containers at room temperature (15-30°C) unless otherwise directed by the manufacturer.
Pharmacology - Pyrantel acts as a depolarizing neuromuscular blocking agent in susceptible parasites, thereby paralyzing the organism. The drug possesses nicotine-like properties and acts similarly to acetylcholine. It also inhibits cholinesterase.
Uses/Indications - Pyrantel has been used for the removal of the following parasites in dogs: ascarids (Toxocara canis, T. leonina), hookworms (Ancylostoma caninum, Uncinaria stenocephala) and stomach worm (Physaloptera). Although not approved for use in cats, it is useful for similar parasites and is considered to be safe to use.
Pyrantel is indicated (labeled) for the removal of the following parasites in horses: Strongylus vulgaris and equinus., Parasacaris equorum, and Probstymayria vivapara. It has variable activity against Oxyuris equi., S. edentatus and small strongyles. Pyrantel is active against ileocecal tapeworm (A. perfoliata) when used at twice the recommended dose.
Although there are apparently no pyrantel products approved for use in cattle, sheep, or goats, the drug is effective (as the tartrate) for the removal of the following parasites: Haemonchus spp., Ostertagia spp., Trichostrongylus spp., Nematodirus spp., Chabertia spp., Cooperia spp. and Oesophagostomum spp..
Pyrantel tartrate is indicated (labeled) for the removal or prevention of the following parasites in swine: large roundworms (Ascaris suum) and Oesophagostomum spp.. The drug also has activity against the swine stomach worm (Hyostrongylus rubidus).
Although not approved, pyrantel has been used in pet birds and llamas. See the Dosage section for more information.
Pharmacokinetics - Pyrantel pamoate is poorly absorbed from the GI tract, thereby allowing it to reach the lower GI in dogs, cats and equines. Pyrantel tartrate is absorbed more readily than the pamoate salt. Pigs and dogs absorb pyrantel tartrate more so than do ruminants, with peak plasma levels occurring 2-3 hours after administration. Peak plasma levels occur at highly variable times in ruminants. Absorbed drug is rapidly metabolized and excreted into the urine and feces.
Contraindications/Precautions/Usage in Pregnancy - Use with caution in severely debilitated animals. The manufacturers usually recommend not administering the drug to severely debilitated animals. Pyrantel is considered to be safe to use during pregnancy and in nursing animals.
Adverse Effects/Warnings - When administered at recommended doses, adverse effects are unlikely. Emesis may occur however, in small animals receiving pyrantel pamoate.
Overdosage/Acute Toxicity - Pyrantel has a moderate margin of safety. Dosages up to approximately 7 times recommended generally result in no toxic reactions. In horses, doses of 20 times those recommended yielded no adverse effects. The LD50 in mice and rats for pyrantel tartrate is 170 mg/kg and is >690 mg/kg for pyrantel pamoate in dogs.
Chronic dosing of pyrantel pamoate in dogs resulted in symptoms when given at 50 mg/kg/day, but not at 20 mg/kg/day over 3 months. Symptoms of toxicity that could possibly be seen include increased respiratory rates, profuse sweating (in animals able to do so), ataxia or other cholinergic effects.
Drug Interactions - Because of similar mechanisms of action (and toxicity), pyrantel is recommended not to be used concurrently with morantel or levamisole. Observation for adverse effects should be intensified if used concomitantly with an organophosphate or diethylcarbamazine. Piperazine and pyrantel have antagonistic mechanisms of action; do not use together.
All doses are for pyrantel pamoate unless otherwise noted. Caution: Listed dosages are often not specified as to whether using the salt or base.
For susceptible parasites:
a) 6.6 mg (as base)/kg PO; 13.2 mg (as base)/kg for cestodes. (Robinson 1987), (Roberson 1988b)
b) 19 mg/kg PO (Brander, Pugh, and Bywater 1982)
c) Pyrantel tartrate: 12.5 mg/kg PO (Roberson 1988b)
Client Information - Shake suspensions well before administering
Dosage Forms/Preparations/FDA Approval Status/Withholding Times -
Pyrantel Pamoate Tablets 22.7 mg (of base), 113.5 mg (of base); Nemex® Tabs (Pfizer); (OTC) Approved for use in dogs.
Pyrantel Pamoate Oral Suspension; 2.27 mg/ml (as base)(for dogs only), 4.54 mg/ml (of base); Nemex®-2 (Pfizer); RFD Liquid Wormer® (Pfizer) (OTC) Approved for use in dogs & cats.
Pyrantel Pamoate Oral Suspension 50 mg/ml (of base); Strongid® T (Pfizer); (OTC) Approved for use in horses not intended for food.
Pyrantel Pamoate Oral Paste 43.9% w/w pyrantel base in 23.6 g (20 ml) paste (180 mg pyrantel base/ml); Strongid® Paste (Pfizer); (OTC) Approved for use in horses not intended for food.
Pyrantel Pamoate Oral Suspension or liquid 50 mg/ml (base) in 30 & 60 ml; Antiminth® (Pfizer) (OTC); Reese’s Pinworm® (Reese) (OTC); Pin-Rid® (Apothecary) (OTC);Pin-X® (Effcon) (OTC)
Pyrantel Capsules 180 mg (equivalent to 62.5 mg pyrantel base); Pin-Rid® (Apothecary) (OTC); Reese's Pinworm® (Reese) (OTC)
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