Mebendazole: 4 Worm Infections Treated & Dosage Guide

Mebendazole, available as

Vermox®

and

Ovex®

, is the most commonly prescribed

anthelmintic

medication in the UK for treating intestinal worm infections, particularly

threadworms

(pinworms), which are the most prevalent worm infection in the country. These parasites enter the body, live in the intestines, and feed off the host, causing symptoms like itchy bottom (pruritus ani). Mebendazole works by preventing worms from absorbing essential sugars (glucose), leading to their starvation and death, while sparing the human host.

About Mebendazole

Mebendazole belongs to the benzimidazole class of anthelmintics, a broad-spectrum medication highly effective against various nematode (roundworm) infestations. It targets common parasites such as

Enterobius vermicularis

(threadworms/pinworms),

Ascaris lumbricoides

(roundworms),

Trichuris trichiura

(whipworms),

Ancylostoma duodenale

and

Necator americanus

(hookworms). Unlike some anthelmintics that paralyze worms, mebendazole specifically inhibits glucose uptake in the parasite’s intestinal cells, depleting their energy reserves without significantly affecting human cells due to poor systemic absorption.

In the UK, threadworm infections are especially common in children and households, spreading easily via contaminated hands, bedding, or surfaces. Mebendazole kills adult worms but not eggs, necessitating hygiene measures to prevent reinfestation. It is available over-the-counter as Ovex® for threadworms in those over 2 years and by prescription for other infections.

Key Types of Worm Infections Treated

• Threadworms (Pinworms): Most common in UK, causing intense anal itching, especially at night. Affects up to 40% of children at some point.
• Roundworms (Ascariasis): Larger worms causing abdominal pain, malnutrition in heavy infections.
• Whipworms (Trichuriasis): Can lead to bloody diarrhea and rectal prolapse in severe cases.
• Hookworms: Cause anemia from blood loss; more common in tropical areas.

How Mebendazole Works

Mebendazole selectively blocks the parasite’s ability to absorb glucose, their primary energy source. This leads to glycogen depletion, reduced ATP production, and eventual worm death. The drug has low oral bioavailability (less than 10%), concentrating in the gut where parasites reside. Dead worms are expelled in feces. It does not kill eggs, so repeat dosing and hygiene are crucial.

Compared to other anthelmintics:

Drug	Mechanism	Examples
Mebendazole, Albendazole	Starves worms (blocks sugar absorption)	Threadworm, roundworm, whipworm
Praziquantel, Ivermectin	Paralyzes worms for expulsion	Tapeworms, some roundworms

Dosage Instructions

Dosage varies by infection type, patient age, and brand (e.g., Vermox™ chewable tablets differ from Emverm™).

For Threadworms (Pinworms)

• Adults and children over 2 years:

  100 mg single dose

  , repeat after 2 weeks to kill hatched eggs. Household members should also be treated.
• Children 6 months–2 years: Use under medical supervision.

For Roundworms, Whipworms, Hookworms

• Adults/children ≥2 years:

  100 mg twice daily

  for 3 days (Emverm™). May repeat in 3 weeks if needed.
• Vermox™:

  500 mg once daily

  for 1 day for roundworms/whipworms (≥1 year).

Chew tablets thoroughly, take with or without food. For young children, crush and mix with food. Treatment duration is short (1–3 days), but follow-up is essential.

Who Can and Cannot Use Mebendazole

Licensed for: Adults and children over 2 years. Often used from 6 months with caution.

Contraindications:

• Children under 6 months without doctor advice.
• Avoid in pregnancy (especially first trimester); use in second/third if essential. Limited data, but animal studies show no major risk.
• Breastfeeding: Avoid or pump/discard milk for 72 hours post-dose due to minimal excretion.
• Hypersensitivity to benzimidazoles.

Consult a doctor for liver disease, as rare hepatotoxicity occurs (elevated enzymes).

Side Effects and Precautions

Mebendazole is generally well-tolerated due to poor absorption. Common side effects (mild, transient):

• Abdominal pain, diarrhea, flatulence, nausea.
• Rash, headache.

Rare/serious (seek medical help):

• Allergic reactions: Hives, swelling, difficulty breathing.
• Liver issues: Jaundice, dark urine (hepatocellular pattern).
• Bone marrow suppression (high/prolonged doses): Neutropenia, thrombocytopenia.
• Severe skin reactions (SJS/TEN), seizures.

Precautions: Maintain strict hygiene—daily showers, short nails, hot wash bedding—to prevent reinfection. No alcohol interaction. Monitor liver function in long-term use.

Preventing Reinfection

Threadworms spread via fecal-oral route. Key steps:

• Wash hands thoroughly, especially after toilet/bedtime.
• Keep fingernails short/clean.
• Discourage nail-biting/thumb-sucking.
• Daily morning showers/baths to remove eggs.
• Wash pajamas, bedding weekly at 60°C.
• Clean toys/handles daily; vacuum floors.
• Treat all household members simultaneously.

When to See a Doctor

• Symptoms persist after treatment.
• Severe abdominal pain, blood in stool, weight loss (possible heavy infection).
• Pregnant/breastfeeding.
• Child under 2 years or recurrent infections.
• Travel-related worms or symptoms like anemia.

Frequently Asked Questions (FAQs)

Q: How quickly does Mebendazole work?

A: Worms die within days; symptoms like itching improve in 1–2 days, but repeat dose after 2 weeks for eggs.

Q: Can I buy Mebendazole over-the-counter?

A: Yes, Ovex® for threadworms (over 2 years) without prescription in UK pharmacies.

Q: Is Mebendazole safe for toddlers?

A: Licensed over 2 years; used from 6 months if doctor-recommended.

Q: Does it treat tapeworms?

A: No, primarily for roundworms. Praziquantel preferred for tapeworms.

Q: What if I miss a dose?

A: Take as soon as remembered; for multi-day regimens, complete course. Consult doctor if unsure.

Further Reading

Explore related topics: Itchy bottom (pruritus ani) and Threadworms for symptoms and prevention.