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Pyrantel Pamoate

Pyrantel pamoate is a pyrimidine-derivative anthelmintic agent.

Uses

Nematode (Roundworm) Infections

Ascariasis and Enterobiasis Pyrantel pamoate is used for the treatment of ascariasis (roundworm infection) caused by Ascaris lumbricoides and enterobiasis (pinworm infection) caused by Enterobius vermicularis. The drug may be used for self-medication of enterobiasis. Pyrantel pamoate has produced cure rates of 85-100% in patients with ascariasis and 90-100% in patients with enterobiasis. Pyrantel pamoate, like albendazole or mebendazole, is considered a drug of choice for ascariasis and enterobiasis. However, pyrantel pamoate has been reported to produce more adverse effects than mebendazole.The efficacy of pyrantel pamoate in the treatment of helminthic infections may vary as a function of GI transit time and the degree of infection. Cure rates may be lower than average in patients who have massive infections and/or hypermotility of the GI tract.

Hookworm Infections

Pyrantel pamoate has been used for the treatment of intestinal hookworm infections caused by Ancylostoma duodenale or Necator americanus, reportedly producing cure rates of 92-96% and 48-93%, respectively, and, like albendazole or mebendazole, is currently considered a drug of choice for these infections. 102, 105 Pyrantel pamoate, like albendazole or mebendazole, is considered a drug of choice for the treatment of eosinophilic enterocolitis caused by Ancylostoma caninum (dog hookworm).

Other Nematode Infections

Pyrantel pamoate has been used with variable results for the treatment of trichostrongyliasis, and is currently considered the drug of choice for the treatment of this infection. Some clinicians state that pyrantel pamoate or albendazole may be effective for the treatment of oesophagostomiasis caused by Oesophagostomum bifurcum.

Moniliformis

Pyrantel pamoate is considered the drug of choice for the treatment of infections caused by Moniliformis moniliformis (thorny-headed worm).

 Diarrhea

Dosage and Administration

Administration

Pyrantel pamoate is administered orally. The drug may be mixed with milk or fruit juice. Special diet, fasting, or purgation prior to administration of pyrantel pamoate is not necessary. Patients should be advised of hygienic precautions needed to minimize reinfection. Patients undertaking self-medication of enterobiasis also should be provided information supplied by the manufacturer that describes dosage information of praziquantel, hygienic precautions needed to minimize reinfection, symptoms of pinworm infections, the worm’s life cycle, and how to locate and identify the worm; the presence of pinworms should be confirmed visually before initiating self-medication.

Dosage

Dosage of pyrantel pamoate is expressed in terms of pyrantel. Dosage of the drug in mg/kg is the same for adults and children. Nematode (Roundworm) Infections For the treatment of ascariasis, enterobiasis, or trichostrongyliasis, the usual dose of pyrantel pamoate in adults and children is 11 mg (of pyrantel) per kg (maximum dose 1 g), given as a single dose; the dose should be repeated after 2 weeks in patients with enterobiasis. The usual dose should also be used for self-medication of enterobiasis in adults and children 2 years of age or older, but a repeat course of therapy should be undertaken only under the direction of a physician. For the treatment of intestinal hookworm infections caused by Ancylostoma duodenale or Necator americanus or for the treatment of eosinophilic enterocolitis caused by Ancylostoma caninum, the recommended dosage for adult and pediatric patients is 11 mg (of pyrantel) per kg (maximum dose 1 g) once daily for 3 consecutive days. A repeat stool examination (using a concentration technique) for eggs of A. duodenale or N. americanus should be performed 2 weeks after treatment and the regimen should be repeated if results are positive. Moniliformis For the treatment of moniliformis, the usual dosage in adults and children is 11 mg (of pyrantel) per kg given once; this dosage should be repeated twice at 2-week intervals.

Cautions

Adverse Effects

Adverse effects of pyrantel pamoate are usually mild, infrequent, and transient, disappearing when the drug is discontinued. The most common adverse effects are GI disturbances, including nausea, vomiting, tenesmus, anorexia, diarrhea, abdominal cramps, and gastralgia. Adverse GI effects may be related to expulsion of the helminths. Other less frequent adverse effects of pyrantel include headache, dizziness, drowsiness, insomnia, rash, fever, and weakness. Minimal, transient increases in serum concentrations of AST (SGOT) have been reported in a small number of patients receiving the drug. Although ototoxicity, optic neuritis, and hallucinations with confusion and paresthesia have been reported rarely, evidence of a causal relationship to the drug is lacking.

Precautions and Contraindications

Patients should be advised to contact a physician if abdominal cramps, nausea, vomiting, diarrhea, headache, or dizziness, which may be associated with pyrantel pamoate use, persists or becomes bothersome. Patients undertaking self-medication of enterobiasis with the drug should be advised to contact a physician if worms other than pinworms are present before or after therapy with the drug or if symptoms of enterobiasis persist. Because minimal, transient increases in serum concentrations of AST (SGOT) have been reported in some patients receiving pyrantel pamoate, the drug should be used with caution in patients with preexisting liver dysfunction; these patients should not undertake self-medication with the drug unless directed by a physician. Pyrantel pamoate should also be used with caution in patients with severe malnutrition or anemia. Ideally, supportive therapy is indicated for anemic, dehydrated, or malnourished patients prior to administration of the drug. Pyrantel pamoate is contraindicated in patients who are hypersensitive to the drug.

Pediatric Precautions

Because of limited experience with pyrantel pamoate in children younger than 2 years of age, the drug should be used in such children only when the potential benefits justify the possible risks. In clinical studies in children receiving a single 11-mg/kg dose of the drug, serum AST concentrations increased transiently in less than 2% of patients; however, in undocumented cases in whom baseline values were not determined, small elevations of AST 24-48 hours after a dose were reported more frequently.

Pyrantel Pamoate

Pregnancy and Fertility

Reproduction studies in animals using pyrantel pamoate have not revealed evidence of harm to the fetus. There also was no evidence of impaired fertility in rats. There are no adequate and controlled studies to date using pyrantel pamoate in pregnant women, and the drug should be used during pregnancy only when clearly needed. Pregnant women considering self-medication with the drug should do so only under the direction of a physician.

Drug Interactions

Piperazine Piperazine and pyrantel pamoate have antagonistic modes of action and, therefore, these drugs should not be administered concomitantly.

Acute Toxcicity

Pyrantel pamoate does not appear to be associated with substantial risk of toxicity following acute oral overdose. No evidence of adverse effect or morphologic change attributable to the drug was apparent in rats receiving oral dosages up to 500 mg/kg daily for 30 days, although slight reductions in growth rate and food consumption were observed in rats receiving 600 mg/kg daily for 13 weeks. Although 2 children have died while receiving pyrantel pamoate, death in these children was not attributable to the drug.

Mechanism of Action

Pyrantel pamoate is a depolarizing neuromuscular blocking agent that exerts its anthelmintic effect via release of acetylcholine and inhibition of cholinesterase, resulting in stimulation of ganglionic (nicotinic) receptors of susceptible helminths. Unlike piperazine, pyrantel produces depolarization of the muscle membrane and increases spike-discharge frequency. The paralyzed worms are expelled from the GI tract by normal peristalsis. Spectrum Pyrantel is active against Enterobius vermicularis (pinworm), Ascaris lumbricoides (roundworm), Ancylostoma duodenale (hookworm), Necator americanus (hookworm), and Trichostrongylus orientalis (hairworm).

Pharmacokinetics

Pyrantel pamoate is poorly absorbed from the GI tract. Following a single oral pyrantel dose of 11 mg/kg, peak plasma concentrations of 50-130 ng/mL occur within 1-3 hours. The absorbed drug is partially metabolized in the liver. Approximately 50% of an oral dose of pyrantel pamoate is excreted unchanged in feces and about 7% is excreted in urine as unchanged drug and its metabolites containing N-methyl-1,-propanediamine.

Chemistry and Stability

Chemistry

Pyrantel pamoate is a pyrimidine-derivative anthelmintic agent. Each 290 mg of pyrantel pamoate is approximately equivalent to 100 mg of pyrantel base. Pyrantel pamoate occurs as a yellow to tan solid and is practically insoluble in water and in alcohol. The commercially available pyrantel pamoate oral suspension has a pH of 4.5-6.

Stability

Commercially available pyrantel pamoate oral suspension should be stored in tight, light-resistant containers at a temperature less than 30°C.

Preparations

Pyrantel Pamoate Oral Suspension 250 mg (of pyrantel) per 5 Antiminth®, mL Pfizer Pin-X®, Effcon Pyrantel Pamoate Suspension, Cypress Liquipharm Reese’s® Pinworm Medicine, (with methylparaben) Reese Tablets 62.5 mg (of pyrantel) Reese’s® Pinworm Medicine Caplets®, Reese AHFS DRUG INFORMATION® (2004)

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