Mebendazole

Overview

Mebendazole is a broad-spectrum benzimidazole anthelmintic used for the treatment of intestinal helminth infections. It is widely prescribed due to its high efficacy, oral administration, and minimal systemic absorption at standard doses, making it generally well tolerated. Mebendazole is included in the World Health Organization’s list of essential medicines and is often used in deworming programs worldwide.

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Pharmacological Class and Formulations

• Class: Anthelmintic (benzimidazole derivative)

• Formulations:

  • Tablets (100 mg)

  • Chewable tablets (100 mg, 500 mg)

  • Oral suspension (100 mg/5 mL, available in some regions)

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Mechanism of Action

Mebendazole binds selectively to β-tubulin of parasitic worms, inhibiting the polymerization of microtubules. This action disrupts cellular processes including glucose uptake and nutrient transport, leading to glycogen depletion, impaired energy metabolism, and eventual parasite death.

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Pharmacokinetics

• Absorption: Poorly absorbed after oral administration; absorption enhanced with fatty meals.

• Distribution: Highly protein-bound; minimal systemic activity at standard doses.

• Metabolism: Extensively metabolized in the liver.

• Elimination: Excreted in urine and bile, mainly as metabolites.

• Half-life: Approximately 3–6 hours (shorter at standard doses).

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Clinical Indications

Intestinal Nematode Infections

• Pinworm (Enterobius vermicularis)

• Roundworm (Ascaris lumbricoides)

• Whipworm (Trichuris trichiura)

• Hookworm (Ancylostoma duodenale, Necator americanus)

Other Uses (Specialist Settings)

• Trichinellosis (higher, prolonged dosing)

• Cystic echinococcosis (hydatid disease) (alternative when albendazole is not available)

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Contraindications

• Hypersensitivity to mebendazole or tablet components

• Pregnancy (particularly first trimester; safety not established)

• Children under 1 year (risk-benefit must be carefully considered)

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Precautions

• Hepatic impairment: Use with caution; drug is metabolized in the liver.

• Pregnancy: Avoid, especially in the first trimester; reserve for cases where benefits outweigh risks.

• Breastfeeding: Small amounts may appear in breast milk; generally considered compatible with caution.

• Pediatric use: Safe in children >1 year at recommended doses.

• Repeated dosing: Monitor liver function and blood counts in prolonged or high-dose regimens.

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Adverse Effects

Common (usually mild and transient)

• Abdominal pain

• Diarrhea

• Flatulence

• Nausea

Less Common

• Rash, pruritus

• Dizziness, headache

Rare but Serious (usually with high or prolonged doses)

• Hepatotoxicity

• Neutropenia, agranulocytosis

• Stevens–Johnson syndrome (very rare)

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Drug Interactions

• Cimetidine: Increases plasma concentrations by reducing metabolism.

• Carbamazepine and phenytoin: Decrease plasma concentrations by enhancing metabolism.

• Metronidazole: Rare reports of severe skin reactions when combined; avoid co-administration.

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Dosage

Adults and Children >2 years

Pinworm (Enterobiasis)

• 100 mg orally once; repeat after 2 weeks if reinfection is suspected.

Roundworm, Whipworm, Hookworm

• 100 mg orally twice daily for 3 days, OR

• 500 mg orally as a single dose (depending on formulation).

Mixed intestinal helminth infections

• 100 mg twice daily for 3 days.

Specialist Indications

Trichinellosis

• 200–400 mg orally three times daily for 3 days, then

• 400–500 mg orally three times daily for 10 days.

Hydatid Disease (Echinococcosis)

• 40–50 mg/kg/day orally in divided doses, up to 3–6 months, under specialist supervision.

Children <2 years

• Use with caution; data limited. Not routinely recommended unless benefit outweighs risk.

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Monitoring

• Short courses: No routine monitoring needed.

• Prolonged therapy: Monitor liver function tests and complete blood counts periodically.

• Clinical follow-up: Stool examination may be used to confirm eradication in persistent or high-risk infections.

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Patient Counseling Points

• Take tablets with water; chewable tablets must be chewed before swallowing.

• A single dose may be sufficient for pinworm, but strict hygiene measures (hand washing, laundering bedding/clothing) are necessary to prevent reinfection.

• Take with food (preferably fatty meals) to enhance absorption when used in systemic infections.

• Report symptoms such as persistent abdominal pain, jaundice, or unusual bruising.

• Treat all household members in cases of pinworm infestation.