Mebendazole is a
synthetic benzimidazole that has a wide spec-trum of antihelminthic activity
and a low incidence of adverse effects.
Less than 10% of
orally administered mebendazole is absorbed. The absorbed drug is protein-bound
(> 90%), is rapidly converted to inactive metabolites (primarily during its
first pass in the liver), and has a half-life of 2–6 hours. It is excreted
mostly in the urine, principally as decarboxylated derivatives. In addition, a
portion of absorbed drug and its derivatives are excreted in the bile.
Absorption is increased if the drug is ingested with a fatty meal.
probably acts by inhibiting microtubule synthe-sis; the parent drug appears to
be the active form. Efficacy of the drug varies with gastrointestinal transit
time, with intensity of infection, and perhaps with the strain of parasite. The
drug kills hookworm, ascaris, and trichuris eggs.
indicated for use in ascariasis, trichuriasis, hook-worm and pinworm
infections, and certain other helminthic infections. It can be taken before or
after meals; the tablets should be chewed before swallowing. For pinworm
infection, the dose is 100 mg once, repeated at 2 weeks. For ascariasis,
trichuriasis, hookworm, and trichostrongylus infections, a dosage of 100 mg twice
daily for 3 days is used for adults and for children older than 2 years of age.
Cure rates are good for pinworm infections and ascariasis, but have been
disappointing in recent studies of trichu-riasis. Cure rates are also lower for
hookworm infections, but a marked reduction in the worm burden occurs in those
not cured. For intestinal capillariasis, mebendazole is used at a dosage of 200
mg twice daily for 21 or more days. In trichinosis, limited reports suggest
efficacy against adult worms in the intestinal tract and tis-sue larvae.
Treatment is three times daily, with fatty foods, at 200–400 mg per dose for 3
days and then 400–500 mg per dose for 10 days; corticosteroids should be coadministered
for severe infections.
mebendazole therapy for intestinal nematodes is nearly free of adverse effects.
Mild nausea, vomiting, diarrhea, and abdom-inal pain have been reported
infrequently. Rare side effects, usually with high-dose therapy, are hypersensitivity
reactions (rash, urti-caria), agranulocytosis, alopecia, and elevation of liver
teratogenic in animals and therefore contrain-dicated in pregnancy. It should
be used with caution in children younger than 2 years of age because of limited
experience and rare reports of convulsions in this age group. Plasma levels may
be decreased by concomitant use of carbamazepine or phenytoin and increased by
cimetidine. Mebendazole should be used with cau-tion in patients with cirrhosis.