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General Description:

Pyrantel, identified by CAS number 15686-83-6, is a notable compound with significant therapeutic applications. Pyrantel is a pyrimidine-derivative anthelmintic agent for the oral treatment of various parasitic worm infections including ascariasis, hookworm infections, enterobiasis (pinworm infection), trichostrongyliasis, and trichinellosis . Pyrantel was initially described in 1965 by researchers from Pfizer who sought cyclic amidines with suitable pharmacokinetic properties (specifically, duration of action) for use as an anthelmintic drug. Pyrantel is mainly available in formulations for dogs and cats as the embonate salt, containing a 34.7% pyrantel base . Pyrantel is on the World Health Organization's List of Essential Medicines, which are the safest and most effective medicines required in a functioning health system , . A depolarizing neuromuscular-blocking agent causing longstanding nicotinic receptor activation, resulting in spastic paralysis of susceptible nematodes (worms). Pyrantel has shown to be effective after a single dose . In humans, it is administered as pyrantel pamoate ,,,.

Indications:

This drug is primarily indicated for: For the treatment of enterobiasis including roundworm (ascariasis), pinworm (enterobius) and hookworm (strongyloides) and hookworm (ancylostoma) in the pyrantel pamoate form . Pyrantel is available in various formulations for humans, dogs, and cats as the pamoate (US Pharmacopeia nomenclature) or embonate (European Pharmacopoeia nomenclature) salt, which contains 34.7% pyrantel base combined with pamoic acid . , . Pyrantel pamoate (embonate) ingested orally is effective for removal and control of ascarid and hookworm infections in puppies and dogs (adult Toxocara canis, Toxascaris leonina, Ancylostoma tubaeforme, An. braziliense, Uncinaria stenocephala), cats (adult Toxocara cati, Toxa. leonina, An. caninum, An. braziliense, U. stenocephala), horses and ponies (adult and immature Parascaris equorum, adult Strongylus vulgaris, S. edentatus, S. equinus, Cyathostomes (Triodontophorus spp, Cyathostomum spp, Cylicodontophorus spp, Cylicocyclus spp, Cylicostephanus spp, Poteriostomum spp.), Oxyuris equi, Anoplocephala perfoliata), swine (adult Ascaris suum, Oesophagostomum dentatum), and humans (adult A. lumbricoides, Enterobius vermicularis, An. duodenale, Necator americanus) . Its use in specific medical scenarios underscores its importance in the therapeutic landscape.

Metabolism:

Pyrantel undergoes metabolic processing primarily in: Pyrantel is administered orally. The poor solubility of the pamoate salt offers the advantage of reduced absorption from the gastrointestinal tract and allows the drug to reach and act against parasites in the large intestine. Metabolism of pyrantel is rapid . The absorbed drug is partly metabolized in the liver . This metabolic pathway ensures efficient processing of the drug, helping to minimize potential toxicity and side effects.

Absorption:

The absorption characteristics of Pyrantel are crucial for its therapeutic efficacy: Pyrantel is poorly absorbed from the GI tract of humans , . Peak serum concentrations occur 1–3 hours after a single dose . The drug's ability to rapidly penetrate into cells ensures quick onset of action.

Half-life:

The half-life of Pyrantel is an important consideration for its dosing schedule: In pigs, following intravenous administration, pyrantel exhibited a half-life of 1.75 +/- 0.19 h . This determines the duration of action and helps in formulating effective dosing regimens.

Route of Elimination:

The elimination of Pyrantel from the body primarily occurs through: Approximately 50% of an oral dose is excreted unchanged in feces; 7% excreted in urine as unchanged drug and metabolites . Understanding this pathway is essential for assessing potential drug accumulation and toxicity risks.

Pharmacodynamics:

Pyrantel exerts its therapeutic effects through: It has similar properties to both competitive and depolarizing neuromuscular blocking agents, which leads to the understanding of the paralytic effect of the drug has on parasites, ultimately resulting in the death of the parasite , . The drug's ability to modulate various physiological processes underscores its efficacy in treating specific conditions.

Mechanism of Action:

Pyrantel functions by: By promoting the release of acetylcholine, inhibiting cholinesterase, and stimulating ganglionic neurons, pyrantel serves as a depolarizing neuromuscular blocking agent in helminths. This causes extensive depolarization of the helminth muscle membrane, resulting in tension to the helminth's muscles, leading to paralysis and release of their attachment to the host organism intestinal walls . This action is unlike piperazine, which is a hyperpolarizing neuromuscular blocking agent that causes relaxation of the helminth muscles, leading to a subsequent detachment from the intestinal wall. Excretion of the parasites in the feces occurs by normal peristalsis . This mechanism highlights the drug's role in inhibiting or promoting specific biological pathways, contributing to its therapeutic effects.

Toxicity:

Classification:

Pyrantel belongs to the class of organic compounds known as hydropyrimidines. These are compounds containing a hydrogenated pyrimidine ring (i.e. containing less than the maximum number of double bonds.), classified under the direct parent group Hydropyrimidines. This compound is a part of the Organic compounds, falling under the Organoheterocyclic compounds superclass, and categorized within the Diazines class, specifically within the Pyrimidines and pyrimidine derivatives subclass.

Categories:

Pyrantel is categorized under the following therapeutic classes: Anthelmintics, Anti-Infective Agents, Antinematodal Agents, Antiparasitic Agents, Antiparasitic Products, Insecticides and Repellents, Central Nervous System Depressants, Drugs that are Mainly Renally Excreted, Neuromuscular Agents, Neuromuscular Blocking Agents, Neuromuscular Depolarizing Agents, Peripheral Nervous System Agents, Pyrimidines, Sulfur Compounds, Tetrahydropyrimidine Derivatives, Thiophenes. These classifications highlight the drug's diverse therapeutic applications and its importance in treating various conditions.

Experimental Properties:

Further physical and chemical characteristics of Pyrantel include:

• Water Solubility: insoluble in water