Pyrantel

Pyrantel is a pyrimidine derivative and anthelmintic for the oral treatment of various parasitic worm infections such as ascariasis, hookworm infections, enterobiasis, trichostrongyliasis and trichinellosis. As a human drug, the active ingredient is formulated as a salt (pamoate or embonate) usually administered in suspensions or chewable tablets. Pyrantel is also commonly used in veterinary medicine for deworming.

Pyrantel was first described in 1965 by researchers at Pfizer, who were searching for cyclic amidines with suitable pharmacokinetic properties (especially duration of action) for use as anthelmintics. Pyrantel is part of the World Health Organization's list of essential medicines.

Pharmacodynamics

Pyrantel acts as a depolarizing neuromuscular blocker, causing sudden contraction and subsequent paralysis of the parasites. This results in the worm losing its hold on the intestinal wall and being eliminated from the system naturally. Pyrantel, as a drug, is always administered in the form of the salt pyrantel pamoate or embonate, which makes it very poorly absorbed in the human intestine. Because of its low absorption and low dosage, pyrantel is considered to be largely safe for humans.

Pharmacokinetics

Pyrantel is absorbed by the human gastrointestinal tract at a very low rate. Approximately 50% of the oral dose is excreted unchanged in the feces. Approximately 7% of the ingested dose is absorbed and excreted in the urine as unchanged drug and metabolites.

Drug Interactions

Concomitant use with piperazine may attenuate the effect of pyrantel.

Side effects

Since the active ingredient is absorbed only to a very small extent, side effects after ingestion are rare.

Possible side effects include:

• Nausea
• Vomiting
• Diarrhea
• Headache
• Dizziness

Toxicological data

LD50, oral, rat: 535 mg/kg