Pyrantel Pamoate
Pyrantel pamoate is a widely used, highly safe **pyrimidine anthelmintic** primarily effective against luminal nematodes, specifically ascarids (roundworms) and hookworms, across a variety of species. Because the pamoate salt is poorly absorbed from the gastrointestinal tract, it achieves high concentrations directly in the gut lumen where the target parasites reside. It is a staple in pediatric veterinary medicine (routinely used in puppies and kittens) due to its exceptionally wide margin of safety and availability in palatable liquid suspensions. > **Clinical Pearl:** While highly effective against roundworms and hookworms, standard doses of pyrantel are ineffective against whipworms (*Trichuris* spp.) and most tapeworms. In horses, however, a double dose is utilized for the control of the ileocecal tapeworm (*Anoplocephala perfoliata*). Resistance in equine strongyles and canine hookworms (*Ancylostoma caninum*) is an emerging clinical concern.
Mechanism: Pyrantel acts as a **depolarizing neuromuscular blocking agent** in susceptible parasites. * It binds selectively to **nicotinic acetylcholine receptors** on the somatic muscle cells of the nematode. * This binding causes continuous depolarization and an influx of calcium โ **spastic paralysis** of the worm. * Paralyzed worms lose their ability to maintain attachment to the host's intestinal mucosa and are subsequently expelled alive in the feces via normal gastrointestinal peristalsis. * It also possesses mild **cholinesterase inhibitory** properties, further contributing to the accumulation of acetylcholine at the parasite's neuromuscular junction.
Dosing by species
- For susceptible parasites ยท Pyrantel tartrate: 25 mg/kg, PO ยท PO ยท Single dose
- For susceptible parasites ยท Pyrantel tartrate: 25 mg/kg, PO ยท PO ยท Single dose
- For susceptible parasites using combination product with praziquantel (Drontal) ยท Administer a minimum dose of 2.27 mg praziquantel and 9.2 mg pyrantel pamoate per pound of body weight according to the dosing tables on labeling. ยท PO ยท Single dose ยท May be given directly by mouth or in a small amount of food. Do not withhold food prior to or after treatment. If reinfection occurs, treatment may be repeated.
- Ascarids, Hookworms, Physaloptera ยท 5 mg/kg, PO; repeat in 2 weeks (one time only for Physaloptera) ยท PO ยท repeat in 2 weeks
- For susceptible parasites ยท 10 mg/kg PO, repeat in 3 weeks ยท PO ยท repeat in 3 weeks
- Kittens ยท 5-10 mg/kg PO; can be repeated every 2-3 weeks until at least 12 weeks of age. ยท PO ยท every 2-3 weeks ยท until at least 12 weeks of age ยท Can be treated as early as 2-3 weeks of age
- For susceptible parasites ยท Pyrantel tartrate: 25 mg/kg, PO ยท PO ยท Single dose
Routes of administration
Contraindications
- Severely debilitated animals
Adverse effects
- Emesis (rare, primarily in small animals)
Drug interactions
- Diethylcarbamazine ยท Increased risk for adverse effects
- Levamisole ยท Because of similar mechanisms of action (and toxicity), do not use concurrently
- Morantel ยท Because of similar mechanisms of action (and toxicity), do not use concurrently
- Organophosphates ยท Increased risk for adverse effects
- Piperazine ยท Pyrantel and piperazine have antagonistic mechanisms of action; do not use together
Monitoring
- Fecal egg count reduction testing (FECRT) for strongyle nematodes (especially in horses to monitor for resistance)
- Resolution of clinical signs of parasitism
- Routine fecal flotations 2-4 weeks post-treatment
Overdose
Pyrantel has a moderate to wide margin of safety. * Dosages up to approximately **7 times** the recommended dose generally result in no toxic reactions. * In horses, doses of **20X** yielded no adverse effects. * The LD50 in mice and rats for pyrantel tartrate is 170 mg/kg; >690 mg/kg for pyrantel pamoate in dogs. * **Chronic dosing** of pyrantel pamoate in dogs resulted in clinical signs when given at 50 mg/kg/day, but not at 20 mg/kg/day over 3 months. * **Clinical signs of toxicity** may include increased respiratory rates, profuse sweating (in species with sweat glands), ataxia, or other cholinergic effects.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.