Antihelminthic Pregnancy: Contraindicated in pregnancy — patients who think they are, or may be, pregnant should not take this preparation. Breast-feeding: limited case-report data show a small amount of mebendazole is present in human milk after oral administration, so caution should be exercised in breast-feeding women.

Mebendazole

Brand names: Vermox, Ovex

Mebendazole is an anthelmintic used most commonly for threadworm (enterobiasis) and for other intestinal worm infections such as roundworm, whipworm and hookworm.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Adults and children over 2 years — trichuriasis, ascariasis and hookworm infections: one 100 mg tablet twice a day for three consecutive days. Enterobiasis (threadworm): a single 100 mg tablet

Route: Oral. Tablets may be chewed or swallowed whole; crush the tablet before giving it to a young child. Oral suspension should be considered for patients such as young children who are unable to swallow the tablet

Frequency: Twice a day for 3 consecutive days (trichuriasis, ascariasis, hookworm); single dose (enterobiasis)

Tablet strength is 100 mg (source product: Vermox 100 mg tablets); the SPC expresses the regimen as 'one tablet'. For enterobiasis it is highly recommended that a second tablet is taken after two weeks if re-infection is suspected. PAEDIATRIC: children over 2 years take the same dose as adults (not weight-based, so paedDose is null). Vermox has not been extensively studied in children below 2 years and no recommendation on a posology can be made for that age group; because of the lack of sufficient safety data it should not be used in children below the age of 1 year, and should be used in children aged 1-2 years only if the potential benefit justifies the potential risk. Always supervise a child while they are taking this medicine. Verify all paediatric use against a children's formulary. US labelling cross-check (VERMOX CHEWABLE 500 mg, a different product): the recommended dosage in patients one year of age and older is one 500 mg chewable tablet as a single dose, chewed completely before swallowing.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

The recommended dosage in patients one year of age and older is one VERMOX™ CHEWABLE 500 mg tablet taken as a single dose. Chew VERMOX™ CHEWABLE 500 mg tablet completely before swallowing. Do not swallow the tablet whole. For patients who have difficulty chewing the tablet, approximately 2 mL to 3 mL of drinking water can be added to a suitably sized spoon and the VERMOX™ CHEWABLE 500 mg tablet placed into the water. Within 2 minutes, the tablet absorbs the water and turns into a soft mass with semi-solid consistency, which can then be swallowed. VERMOX™ CHEWABLE 500 mg tablet can be taken without regard to food intake [see Clinical Pharmacology (12.3) ]. The recommended dosage in patients …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2021-10-05. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

Pregnancy
Hypersensitivity to the product or any of its components

Side effects

Gastrointestinal — abdominal pain (common); abdominal discomfort, diarrhoea, flatulence (uncommon); nausea, vomiting (rare)
Skin — rash (uncommon); toxic epidermal necrolysis, Stevens-Johnson syndrome, exanthema, angioedema, urticaria, alopecia (rare)
Blood — neutropenia (uncommon); agranulocytosis (rare, observed in patients treated for echinococcosis)
Hepatobiliary — hepatitis and abnormal liver function tests (rare)
Nervous system — convulsions (rare; reported very rarely post-marketing in children including infants below 1 year), dizziness; hypersensitivity including anaphylactic and anaphylactoid reactions; glomerulonephritis (rare, in echinococcosis)

Interactions

Cimetidine — may inhibit the hepatic metabolism of mebendazole, resulting in increased plasma concentrations
Metronidazole — concomitant use should be avoided; a case-control study of an outbreak of Stevens-Johnson syndrome / toxic epidermal necrolysis suggested a possible association with concomitant use

Clinical monograph

How it works

It binds to parasite tubulin and inhibits microtubule formation, impairing glucose uptake and energy metabolism in the worm, leading to its death.

Prescribing in practice

Use with caution and generally avoid in pregnancy, particularly the first trimester; check current prescribing references before use in pregnancy or breastfeeding.
For threadworm, treat all household members at the same time, as reinfection is common.
Combine drug treatment with hygiene measures and repeat the dose after about two weeks to cover reinfection.

Monitoring

No routine monitoring is required for single-dose threadworm treatment; for prolonged high-dose use in other infections, follow the SPC for relevant safety checks.

Counselling the patient

Everyone in the household should be treated together, even if they have no symptoms.
Alongside the medicine, wash hands and nails, launder bedclothes and nightwear, and keep nails short to prevent reinfection.
A second dose after about two weeks is usually advised to catch any reinfection.

Evidence & guidelines

First-line for threadworm with hygiene measures (NICE CKS threadworm).

Reference: NICE CKS; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Pathways