Common name: PYRANTEL

Type: veterinary medecine
Chemical class: tetrahydropyrimidine

CHEMICAL STRUCTURE

Molecular structure of PYRANTEL 

 


EFFICACY AGAINST PARASITES

Type of action: Anthelmintic nematicide, endoparasiticide.
Main veterinary parasites controlled: Gastrointestinal roundworms = nematodes

Efficacy against a specific parasite depends on the delivery form and on the dose administered.

Click here for general information on features and characteristics of PARASITICIDES.


DOSING

Click here to view the article in this site with the most common dosing recommendations for pyrantel used in domestic animals.

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SAFETY

Oral LD50, rat, acute*: pamoate=embonate >5000 mg/kg; tartrate 170 mg/kg
Dermal LD50, rat, acute*: not found
* These values refer to the active ingredient. Toxicity has to be determined for each formulation as well. Formulations are usually significantly less toxic than the active ingredients.

MRL (maximum residue limit) established for either beef, mutton pork or chicken meat*:

  • CODEX: No
  • EU: No (Annex II)
  • USA: Yes
  • AUS: No

* For any of the usual salts. This information is an indicator of the acceptance of an active ingredient by the most influential regulatory bodies for use on livestock.

Withholding periods for meat, milk, eggs, etc. depend on delivery form, dose and national regulations. Check the product label in your country.

Learn more about pyrantel safety.

General safety information for antiparasitics is available in specific articles in this site (click to visit):

WARNING

Never use products for livestock on dogs and cats, unless they are explicitly approved for both livestock and pets. Pets may not tolerate livestock formulations.

It is obvious that veterinary products are not intended for and should never be used on humans!!!


MARKETING & USAGE

Decade of introduction: 1960
Introduced by: PFIZER → ZOETIS
Some original brands: BANMINTH, EXHELM, STRONGID
Patent: Expired (particular formulations may be still patent-protected)

Use in LIVESTOCK: Yes, scarce
Use in HORSES: Yes, very abundant
Use in DOGS and CATS: Yes, a lot

Main delivery forms: 

Use in human medicine: Yes
Use in public/domestic hygiene: No
Use in agriculture: No
Generics available: Yes, a lot

SELECTION OF COMMERCIAL BRANDS FOR PETS WITH PYRANTEL

With pyrantel alone

With pyrantel + ivermectin

With pyrantel + praziquantel

With pyrantel + other anthelmintics


PARASITE RESISTANCE

In livestock & horses: Yes, in pigs (Oesophagostomum spp) and horses (Cyathostomins), apparently cross-resistance with levamisole.
In pets: Yes, in dogs (Ancylostoma caninum)

Learn more about parasite resistance and how it develops.


SPECIFIC FEATURES

Pyrantel is a veteran, narrow-spectrum nematicide closely related to morantel and oxantel, all belonging to the tetrahydropyrimidines. It is mostly used in the form of salts (citrate, embonate, pamoate, tartrate, etc.).

It is used a lot in dogs and cats in the form of drenches or tablets, pills, etc, against various roundworms, mostly in combination with other a larger spectrum nematicides (e.g. ivermectin, febantel) or with a taenicide (e.g. praziquantel).

It is very scarcely used in livestock, mainly in pigs in the form of feed additives. It is also abundantly used in horses.

It is also used in human medicines against various gastrointestinal roundworms.

Efficacy of pyrantel

Pyrantel is highly effective against gastrointestinal nematodes, especially those of dogs and cats (e.g. those of the genus Ancylostoma, Toxocara, Toxascaris, Uncinaria, etc.). However, efficacy against immature stages is only ensured if present in the intestinal lumen. Stages in the tissues as e.g. arrested larvae are only insufficiently controlled or not at all.

Unless delivered using a slow-release device, pyrantel has no residual effect. This means that a single administration will kill the parasites present in the host at the time of treatment, but it will not protect the host against re-infestations. To ensure the control of certain parasites re-treatments may be required.

It has no efficacy whatsoever against other non-gastrointestinal roundworms (pulmonary, skin, eyes, etc.), flukes (i.e. trematodes), and tapeworms (i.e. cestodes).

Pharmacokinetics of pyrantel

After oral administration pyrantel pamoate is poorly absorbed in the gut in dogs, cats and horses. This allows that high concentrations of unchanged drug reach the large intestine. Pyrantel tartrate is better absorbed into the bloodstream, especially in animals with a simple stomach (e.g. dogs, cats, pigs, horses). This reduces the time it remains in the gastrointestinal system and reduces the efficacy against gastrointestinal worms, especially against those species in the large intestine (e.g. Trichuris spp). For this reason, in non-ruminants the pamoate salt is preferred, which is less absorbed and allows higher safety margins of >7.

Absorbed pyrantel is quickly metabolized in the liver. In dogs 40% of the administered dose is excreted through urine, in pigs about 34%, most of it in the form of metabolites. In cattle 70% of the administered dose is excreted through feces, mainly as unchanged pyrantel. It is also partly excreted with the milk.

Influence of diet. In pigs, pyrantel citrate administered together with a fiber-poor diet shows a slower stomach passage, and therefore a longer absorption period, which increases its anthelmintic bioavailability. In dogs, administration of pyrantel with the food also increases the time in the stomach and its bioavailability.

Mechanism of action of pyrantel

Tetrahydropyrimidines, including pyrantel, act on the nervous system of the worms as inhibitors of acetylcholinesterase (also known as AchE), an enzyme that hydrolyzes acetylcholine (Ach). Ach is a molecule involved in the transmission of nervous signals from nerves to muscles (so-called neuromuscular junctions) and between neurons in the brain (so-called cholinergic brain synapses). AchE's role is to terminate the transmission of nervous signals where acetylcholine is the neurotransmitter (there are several other neurotransmitters). Inhibition of AchE massively disturbs the normal movements of the parasites.

The bottom line for the parasitic worms is that they are paralyzed and die more or less quickly or are expelled from the gut because they cannot keep themselves attached to the intestinal wall.

Click here to view the list of all technical summaries of antiparasitic active ingredients in this site.

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