Pyrantel Pamoate

PYRANTEL PAMOATE

Pyrantel pamoate is a broad-spectrum antihelminthic highly effective for the treatment of pinworm, ascaris, and Trichostrongylusorientalis infections. It is moderately effective against both speciesof hookworm. It is not effective in trichuriasis or strongyloidiasis. Oxantel pamoate, an analog of pyrantel not available in the USA, has been used successfully in the treatment of trichuriasis; the two drugs have been combined for their broad-spectrum antihelmint-hic activity.

Basic Pharmacology

Pyrantel pamoate is a tetrahydropyrimidine derivative. It is poorly absorbed from the gastrointestinal tract and active mainly against luminal organisms. Peak plasma levels are reached in 1–3 hours. Over half of the administered dose is recovered unchanged in the feces.

Pyrantel is effective against mature and immature forms of susceptible helminths within the intestinal tract but not against migratory stages in the tissues or against ova. The drug is a neuro-muscular blocking agent that causes release of acetylcholine and inhibition of cholinesterase; this results in paralysis of worms, which is followed by expulsion.

Clinical Uses

The standard dose is 11 mg (base)/kg (maximum, 1 g), given orally once with or without food. For pinworm, the dose is repeated in 2 weeks, and cure rates are greater than 95%. The drug is available in the USA without prescription for this indication.

For ascariasis, a single dose yields cure rates of 85–100%. Treatment should be repeated if eggs are found 2 weeks after treat-ment. For hookworm infections, a single dose is effective against light infections; but for heavy infections, especially with Necatoramericanus, a 3-day course is necessary to reach 90% cure rates. Acourse of treatment can be repeated in 2 weeks.

Adverse Reactions, Contraindications, & Cautions

Adverse effects are infrequent, mild, and transient. They include nausea, vomiting, diarrhea, abdominal cramps, dizziness, drowsiness, headache, insomnia, rash, fever, and weakness. Pyrantel should be used with caution in patients with liver dys-function, because low, transient aminotransferase elevations have been noted in a small number of patients. Experience with the drug in pregnant women and children younger than 2 years of age is limited.