Benzimidazole Antihelminthics

Benzimidazole antihelminthics bind parasite beta-tubulin, blocking microtubule formation, glucose uptake and egg development. Albendazole and mebendazole treat intestinal nematodes, and albendazole also treats tissue infections because its sulphoxide metabolite is systemically active. Triclabendazole is used for fascioliasis.

Pharmacokinetics. Albendazole is poorly absorbed, and a fatty meal raises levels 4 to 5 times; it is converted in the liver to active albendazole sulphoxide (half-life 8 to 12 hours). Mebendazole is minimally absorbed and acts in the gut. Triclabendazole is absorbed with food.

• Albendazole: broadest use, intestinal and tissue infections.
• Mebendazole: intestinal nematodes only; not for tissue disease.
• Triclabendazole: fascioliasis, 10 mg/kg single dose (or two doses 12 to 24 hours apart for severe infection).

Albendazole (adult).

• Ascaris, hookworm, Enterobius: 400 mg single dose (repeat in 2 weeks for Enterobius). Trichuris: 400 mg daily for 3 days.
• Giardiasis: 400 mg daily for 5 days.
• Neurocysticercosis: 15 mg/kg daily in two doses (maximum 800 mg daily) for 10 to 14 days, with prednisolone 1 mg/kg daily started before and during treatment, and antiseizure medicine.
• Hydatid disease: 400 mg twice daily with food, for 1 to 6 months (cycles of 28 days with a 14-day break), around surgery or puncture-aspiration-injection-reaspiration.
• Toxocariasis: 400 mg twice daily for 5 days.

Mebendazole. 500 mg single dose, or 100 mg twice daily for 3 days.

Children. Albendazole 400 mg single dose from age 2 years (200 mg from 12 to 23 months); mebendazole 500 mg single dose from 1 year.

Region. In East Africa, school-based mass deworming programmes use a single albendazole 400 mg dose. Neurocysticercosis is treated only after brain imaging, and not in the presence of untreated hydrocephalus or ocular cysts.

Contraindications. Hypersensitivity; pregnancy in the first trimester; albendazole in untreated hydrocephalus or ocular cysticercosis.

Serious adverse effects. Hepatotoxicity, leukopenia and pancytopenia (rare, mainly with prolonged courses), alopecia, headache, abdominal pain. In neurocysticercosis, inflammatory reaction to dying cysts causes seizures and headache.

Monitoring. Liver enzymes and full blood count before and every 2 weeks during courses over 14 days; stop for ALT more than 5 times the upper limit of normal or neutropenia.

Interactions. Phenytoin, carbamazepine and phenobarbital lower levels. Cimetidine, dexamethasone, praziquantel and a fatty meal raise levels.

Common prescribing errors. Giving albendazole on an empty stomach for tissue infection; treating neurocysticercosis without steroids; missing pregnancy; prolonged courses without blood tests.

Special groups.

• Pregnancy: albendazole and mebendazole after the first trimester in endemic areas; avoid in the first trimester unless the benefit is clear.
• Breastfeeding: compatible.
• Liver disease: avoid prolonged albendazole.
• Kidney impairment: no change.

Referral and escalation. Refer neurocysticercosis, hydatid cysts, hepatotoxicity, and cytopenias.