Mebendazole

Mebendazole is an oral benzimidazole anthelmintic used for roundworm, hookworm, whipworm and pinworm infections. It is poorly absorbed, so it acts mainly in the gut, with fewer systemic effects than albendazole, and it is not suitable for tissue infections. Cure rates with a single dose are poor for whipworm and hookworm.

Class. Anthelmintic; benzimidazole.

Mechanism. Binds beta-tubulin and blocks microtubule formation, impairing glucose uptake in the worm.

Pharmacokinetics. Absorption under 10%, increased by fatty food. Extensive first-pass metabolism. Half life 3 to 6 hours. Excreted in faeces and urine.

Ascariasis, hookworm, trichuriasis (adults and children 1 year and over). 100 mg orally twice daily for 3 days; or 500 mg as a single dose (lower cure rates for hookworm and trichuriasis).

Enterobiasis. 100 mg single dose, repeated after 2 weeks.

Mass drug administration. 500 mg single dose in school-based programmes.

Loading dose, maintenance dose and titration. Not applicable. Maximum: 500 mg in a single dose, or 200 mg daily for 3 days.

Main alternatives. Albendazole.

Contraindications. Hypersensitivity; first trimester of pregnancy.

Serious adverse effects. Stevens-Johnson syndrome and toxic epidermal necrolysis (rare), neutropenia and agranulocytosis at high doses, and hepatitis (rare).

Common adverse effects. Abdominal pain, diarrhoea, flatulence and passage of worms.

Interactions. Metronidazole: increases risk of severe skin reactions (avoid); cimetidine raises levels; carbamazepine and phenytoin lower levels.

Common prescribing errors. Using a single dose for whipworm and expecting cure, giving in the first trimester, and using it for tissue infections.

Special groups. - Pregnancy: avoid in the first trimester. - Breastfeeding: compatible. - Children: from 1 year. - Older adults: usual dose. - Kidney impairment: no adjustment. - Liver impairment: caution in severe disease.

Regional points. Single-dose mebendazole is used in routine school deworming in East Africa, but albendazole is more widely supplied.

Formulations. Chewable tablets 100 mg and 500 mg; suspension 100 mg/5 mL.

Administration. Chew or crush tablets; with or without food.

Baseline. Diagnosis by stool microscopy where available; pregnancy status.

Monitoring. Egg clearance on repeat stool test 2 to 4 weeks after in selected patients; symptoms.

Stopping thresholds. Stop for severe skin reaction.

Referral and escalation. Specialist review for persistent infection, heavy worm burden with obstruction, and tissue disease.