Mebendazole Description

Mebendazole is a (synthetic) broad-spectrum anthelmintic available as chewable tablets, each containing 100 mg of Mebendazole. Inactive ingredients are: anhydrous lactose NF, corn starch, magnesium stearate, microcrystalline cellulose, sodium lauryl sulfate, sodium saccharin, sodium starch glycolate, stearic acid, and FD&C Yellow #6.

Mebendazole is methyl 5-benzoylbenzimidazole-2-carbamate and has the following structural formula:

Molecular Formula: C16H13N3O3

Mebendazole is a white to slightly yellow powder with a molecular weight of 295.29. It is less than 0.05% soluble in water, dilute mineral acid solutions, alcohol, ether and chloroform, but is soluble in formic acid.

Mebendazole - Clinical Pharmacology

Following administration of 100 mg twice daily for three consecutive days, plasma levels of Mebendazole and its primary metabolite, the 2-amine, do not exceed 0.03 mcg/mL and 0.09 mcg/mL, respectively. All metabolites are devoid of anthelmintic activity. In man, approximately 2% of administered Mebendazole is excreted in urine and the remainder in the feces as unchanged drug or a primary metabolite.

Mode of Action

Mebendazole inhibits the formation of the worms' microtubules and causes the worms' glucose depletion.

Indications and Usage for Mebendazole

Mebendazole tablets are indicated for the treatment of Enterobius vermicularis (pinworm), Trichuris trichiura (whipworm), Ascaris lumbricoides (common roundworm), Ancylostoma duodenale (common hookworm), Necator americanus (American hookworm) in single or mixed infections.

Efficacy varies as a function of such factors as preexisting diarrhea and gastrointestinal transit time, degree of infection, and helminth strains. Efficacy rates derived from various studies are shown in the table below:

Contraindications

Mebendazole is contraindicated in persons who have shown hypersensitivity to the drug.

Warnings

There is no evidence that Mebendazole, even at high doses, is effective for hydatid disease. There have been rare reports of neutropenia and agranulocytosis when Mebendazole was taken for prolonged periods and at dosages substantially above those recommended.

Precautions

General

Periodic assessment of organ system functions, including hematopoietic and hepatic, is advisable during prolonged therapy.

Information for Patients

Patients should be informed of the potential risk to the fetus in women taking Mebendazole during pregnancy, especially during the first trimester (See Pregnancy).

Patients should also be informed that cleanliness is important to prevent reinfection and transmission of the infection.

Drug Interactions

Preliminary evidence suggests that cimetidine inhibits Mebendazole metabolism and may result in an increase in plasma concentrations of Mebendazole.

Carcinogenesis, Mutagenesis, Impairment of Fertility

In carcinogenicity tests of Mebendazole in mice and rats, no carcinogenic effects were seen at doses as high as 40 mg/kg (one to two times the human dose, based on mg/m2) given daily over two years. Dominant lethal mutation tests in mice showed no mutagenicity at single doses as high as 640 mg/kg (18 times the human dose, based on mg/m2). Neither the spermatocyte test, the F1 translocation test, nor the Ames test indicated mutagenic properties. Doses up to 40 mg/kg in mice (equal to the human dose, based on mg/m2), given to males for 60 days and to females for 14 days prior to gestation, had no effect upon fetuses and offspring, though there was slight maternal toxicity.

Pregnancy

Pregnancy category C

Mebendazole has shown embryotoxic and teratogenic activity in pregnant rats at single oral doses as low as 10 mg/kg (approximately equal to the human dose, based on mg/m2). In view of these findings the use of Mebendazole is not recommended in pregnant women. Although there are no adequate and well-controlled studies in pregnant women, a postmarketing survey has been done of a limited number of women who inadvertently had consumed Mebendazole during the first trimester of pregnancy. The incidence of spontaneous abortion and malformation did not exceed that in the general population. In 170 deliveries on term, no teratogenic risk of Mebendazole was identified.

Nursing Mothers

It is not known whether Mebendazole is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when Mebendazole is administered to a nursing woman.

Pediatric Use

The drug has not been extensively studied in children under two years; therefore, in the treatment of children under two years the relative benefit/risk should be considered.