Singapore Drugs Database

Indication

For the treatment of enterobiasis including roundworm (ascariasis), pinworm (enterobius) and hookworm (strongyloides) and hookworm (ancylostoma) in the pyrantel pamoate form [L1893]. 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 [L1893]. [L1900], [A32283]. 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) [L1900].

Mechanism of Action

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 [L1893]. 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 [L1892].

Pharmacokinetics

Absorption

Pyrantel is poorly absorbed from the GI tract of humans [L1893], [L1908]. Peak serum concentrations occur 1–3 hours after a single dose [L1904].

Distribution

Metabolism

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 [L1991]. The absorbed drug is partly metabolized in the liver [L1907].

Elimination

Toxicity

Mild adverse effects include nausea, vomiting, diarrhea, headache, and dizziness [L1893]. LD50 in rats is 535 mg/kg [L1895]. Reported effects in humans in case of overdose include gastrointestinal disturbance, central nervous system effects, and superficial skin reactions. In one study, serum aspartate aminotransferase (AST) and serum alanine-aminotransferase (ALT) values were increased in approximately 2% of patients [L1906]. Pyrantel should be used with caution in patients with severe malnutrition or anemia. Supportive therapy is recommended for anemic, dehydrated, or malnourished patients before administration of the drug [L1898]. Pyrantel pamoate has been placed in pregnancy category C. This refers to the fact that animal studies have revealed adverse effects on the fetus (teratogenic/embryocidal, or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus [L1894].Data on the use of pyrantel pamoate in pregnant women are quite limited. In mass treatment programs for which the World Health Organization (WHO) has observed that the benefits of treatment outweigh the risks, WHO allows the use of pyrantel pamoate in the 2nd and 3rd trimesters of pregnancy, due to the fact that the effects of pyrantel on birth outcome are uncertain. The risk of treatment in pregnant women already known to have an infection needs to be balanced with the risk of disease progression if treatment were to be omitted [L1894]. Individuals with liver disease are more susceptible to the toxicity in cases of pyrantel overexposure [L1894], [L1897]. There are no data regarding the presence of pyrantel in breast milk. Pyrantel is poorly absorbed from the GI tract; therefore, excretion into breast milk may be minimal. Some experts recommend that a single dose of pyrantel therapy may be given to breastfeeding women [L1893].

Active Ingredient/Synonyms

pirantel | pyrantel | Pyrantelum | Pyrantel |