Pyrantel Pamoate — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	5 mg/kg (based on pyrantel base)	Single dose; repeat in 2-4 weeks for roundworms, or as directed for hookworms	Duration: Usually single administration; may be repeated for severe infections Notes: Administer with food to reduce risk of vomiting. For puppies, start at 2 weeks of age and repeat every 2 weeks until 12 weeks old, then monthly until 6 months.
Cat	PO	5 mg/kg (based on pyrantel base)	Single dose; repeat in 2-4 weeks for roundworms, or as directed for hookworms	Duration: Usually single administration; may be repeated for severe infections Notes: Administer with food to reduce risk of vomiting. For kittens, start at 3 weeks of age and repeat every 2 weeks until 12 weeks old, then monthly until 6 months.
Horse	PO	6.6 mg/kg (based on pyrantel pamoate) or 2.64 mg/kg (based on pyrantel tartrate) for daily use	Single dose for therapeutic use; daily for continuous control	Duration: Single dose; repeat as needed based on fecal egg counts Notes: For daily use, pyrantel tartrate is often used in feed. For pamoate, administer as a paste or suspension.
Cattle	PO	Not established; extra-label use may be 5-10 mg/kg	Single dose	Duration: Single administration Notes: Not approved; use with caution and consult a veterinarian. Other anthelmintics are preferred.
Small Ruminants (Sheep/Goats)	PO	Not established; extra-label use may be 5-10 mg/kg	Single dose	Duration: Single administration Notes: Not approved; use with caution and consult a veterinarian. Other anthelmintics are preferred.
Rabbit	PO	5-10 mg/kg	Single dose; may repeat in 2 weeks	Duration: Single administration Notes: Use with caution; not FDA-approved. Compounded formulations may be needed.
Bird/Poultry	PO	Not established; extra-label use may be 5-10 mg/kg	Single dose	Duration: Single administration Notes: Not approved; use with caution and consult a veterinarian.
Exotic/Other	PO	Variable; consult a specialist	Variable	Duration: Variable Notes: Dosing should be based on species-specific references and veterinary guidance.

Clinical Indications & Species Uses

General Indications

Treatment of susceptible gastrointestinal nematode infections in companion animals, primarily dogs and cats.

Dog (Canine)

Treatment of roundworms (Toxocara canis, Toxascaris leonina)
Treatment of hookworms (Ancylostoma caninum, Ancylostoma braziliense, Uncinaria stenocephala)

Cat (Feline)

Treatment of roundworms (Toxocara cati)
Treatment of hookworms (Ancylostoma tubaeforme, Ancylostoma braziliense)

Horse (Equine)

Treatment of large strongyles (Strongylus vulgaris, S. edentatus, S. equinus)
Treatment of small strongyles (Cyathostomum spp.)
Treatment of roundworms (Parascaris equorum)
Treatment of pinworms (Oxyuris equi)

Rabbit & Small Mammals

Treatment of pinworms (Passalurus ambiguus) and roundworms (e.g., Obeliscoides cuniculi) in some cases, but not FDA-approved.

Exotic & Other Species

Treatment of gastrointestinal nematodes in various exotic species (e.g., reptiles, small mammals) on a case-by-case basis, but not approved.

Pharmacology & Mechanism of Action

Drug Class: Anthelmintic | Pharmacological Group: Tetrahydropyrimidine derivative

Mechanism of Action: Pyrantel pamoate acts as a depolarizing neuromuscular blocking agent in susceptible nematodes. It binds to nicotinic acetylcholine receptors (nAChRs) on the muscle cells of the parasite, causing persistent depolarization and spastic paralysis. The paralyzed worms are then expelled from the host via normal peristalsis. The drug is selective for parasite nAChRs over mammalian receptors, providing a wide margin of safety.

Pharmacodynamics: Pyrantel pamoate is effective against adult and immature stages of many gastrointestinal nematodes, including roundworms (Toxocara canis, Toxascaris leonina) and hookworms (Ancylostoma spp., Uncinaria stenocephala) in dogs and cats. It has limited activity against whipworms (Trichuris vulpis) and tapeworms. The drug acts rapidly, with paralysis of worms occurring within minutes of exposure. It is not effective against migrating larval stages or tissue-dwelling parasites.

⚡ Pharmacokinetics Summary

Absorption: Pyrantel pamoate is poorly absorbed from the gastrointestinal tract, with less than 15% of an oral dose absorbed systemically in most species. The majority of the drug remains in the lumen of the gut to exert its local anthelmintic effect.

Distribution: Due to poor absorption, systemic distribution is minimal. The small amount absorbed is distributed widely in tissues, but concentrations are low and not clinically significant.

Metabolism: The absorbed fraction is rapidly metabolized in the liver to inactive metabolites, primarily via oxidation and conjugation.

Excretion: Unabsorbed pyrantel pamoate is excreted in feces. Absorbed drug and its metabolites are excreted in urine and bile. In ruminants, a significant portion may be metabolized by ruminal microorganisms.

Half-Life: The plasma half-life is short, approximately 1-2 hours in dogs and cats, but due to local action, the clinical effect persists for several days.

Bioavailability: Oral bioavailability is low (<15%) due to poor absorption and first-pass metabolism.

Protein Binding: Protein binding is low, approximately 20-30% in plasma.

Available Formulations & Strengths

Oral Tablet 50 mg (as pyrantel pamoate), 100 mg, 250 mg (PO)

Oral Suspension 50 mg/mL (as pyrantel pamoate) (PO)

Oral Paste (Horse) 18.5% (w/w) pyrantel pamoate (PO)

Feed Additive (Horse) Pyrantel tartrate 2.64 mg/g (PO)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to pyrantel or any component of the formulation
Hepatic disease (severe)
Concurrent use with piperazine (antagonistic effect)
Use in severely debilitated animals or those with intestinal obstruction

Warnings & Clinical Precautions:

Use with caution in animals with hepatic impairment.
In horses, do not use in foals under 4 weeks of age unless directed by a veterinarian.
In dogs and cats, use with caution in very young animals (under 2-3 weeks) and in pregnant or lactating animals; safety not fully established.
Do not use in animals with known hypersensitivity.
For food animals, observe withdrawal times.
Avoid use in animals with severe malnutrition or dehydration.
In ruminants, use is extra-label; consult a veterinarian for appropriate withdrawal times.

Adverse Effects & Reactions

Common:

Vomiting (especially in cats)
Diarrhea
Anorexia
Lethargy

Serious / Severe:

Allergic reactions (rare)
Ataxia (at high doses)
Muscle tremors (at high doses)

Rare:

Hepatotoxicity (reported in dogs with high doses)
Neurological signs (in overdose)

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Piperazine	Antagonistic effect; piperazine causes paralysis of worms, while pyrantel causes spastic paralysis, so concurrent use may reduce efficacy.	Moderate
Levamisole	Additive toxicity; both are cholinergic agonists, may increase risk of nicotinic toxicity.	Moderate
Organophosphates	Additive cholinesterase inhibition; may increase risk of toxicity.	High
Depolarizing neuromuscular blockers (e.g., succinylcholine)	Additive neuromuscular blockade; may enhance effects.	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Vomiting
Diarrhea
Ataxia
Muscle tremors
Weakness
Respiratory depression (severe)

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Induce vomiting if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids for dehydration and electrolyte imbalances. Monitor respiratory and cardiac function. In severe cases, atropine may be used to counteract muscarinic effects, but it will not reverse nicotinic effects. Diazepam may be used for seizures.

Food Animal Withdrawal Times

🥩 Meat: 0 days🥛 Milk: 0 days🥚 Eggs: 0 days

Pyrantel pamoate is not approved for food animals in the US. For extra-label use in food animals, a withdrawal time of at least 14 days for meat and 4 days for milk is recommended, but consult a veterinarian and follow local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 15°C-30°C (59°F-86°F).

Handling & Special Conditions: Protect from moisture. Keep container tightly closed. Do not freeze oral suspensions.

Dispensing Status: Over-The-Counter (OTC)

Approval Status: Approved for use in dogs, cats, and horses. Not approved for food animals in the US.

Extra-Label (Off-Label) Use: In the US, pyrantel pamoate is available over-the-counter for dogs and cats. For food animals, extra-label use is permitted under AMDUCA only with a valid veterinary-client-patient relationship and must follow withdrawal times.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Pyrantel pamoate is a safe and effective anthelmintic for the treatment of roundworms and hookworms in dogs and cats. It is often used in puppies and kittens due to its wide margin of safety. It is also used in horses for control of strongyles and ascarids. Because it is poorly absorbed, systemic side effects are rare. However, it is not effective against whipworms or tapeworms, so a fecal examination is recommended to guide therapy. For heartworm prevention, pyrantel is often combined with other drugs (e.g., ivermectin). In food animals, its use is limited and other anthelmintics are preferred. Always follow label directions and consult a veterinarian for appropriate dosing and withdrawal times.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)