1. Clinical Overview
Mebendazole is a broad-spectrum benzimidazole anthelmintic agent used primarily for the treatment of intestinal helminth infections. It acts by selectively and irreversibly inhibiting microtubule synthesis in parasitic cells, leading to glucose depletion and eventual death of the helminth. In the Indian context, it is a first-line treatment for common soil-transmitted helminthiases (STH) like ascariasis, trichuriasis, and hookworm infections, which are endemic in many regions due to poor sanitation.
| Onset | Duration | Bioavailability |
|---|---|---|
| Parasite death begins within 24-48 hours, but expulsion from the gastrointestinal tract may take 2-3 days. | The anthelmintic effect is sustained, with a single dose often sufficient for cure. Plasma half-life is 2.5-5.5 hours, but its effect on parasites is prolonged. | Approximately 2-10% due to poor systemic absorption. Absorption is significantly enhanced (up to 50%) when taken with a high-fat meal. |
2. Mechanism of Action
Mebendazole binds selectively and with high affinity to beta-tubulin of parasitic helminths, inhibiting its polymerization into microtubules. This disrupts the cytoplasmic microtubule network, which is essential for numerous cellular processes including glucose uptake, intracellular transport, and structural integrity.
3. Indications & Uses
- Ascariasis (Roundworm infection)
- Trichuriasis (Whipworm infection)
- Hookworm infections (Ancylostoma duodenale and Necator americanus)
- Enterobiasis (Pinworm infection)
4. Dosage & Administration
Adult Dosage: For common STH (Ascaris, Trichuris, Hookworm): 100 mg twice daily for 3 consecutive days. For Enterobiasis (Pinworm): A single 100 mg dose, repeated after 2 weeks.
Administration: Tablet can be chewed, swallowed whole, or crushed and mixed with food. For optimal absorption in systemic infections (off-label), administer with a high-fat meal. For intestinal infections, timing with food is less critical but can be taken with meals to reduce GI upset.
5. Side Effects
Common side effects may include:
- Transient abdominal pain
- Diarrhea
- Flatulence
- Nausea
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Carbamazepine, Phenytoin | Significantly reduces plasma levels of mebendazole via CYP450 induction, potentially reducing efficacy. | Major |
| Cimetidine | May increase plasma levels of mebendazole by inhibiting CYP450 metabolism. | Moderate |
| Metronidazole | Theoretical risk of Stevens-Johnson Syndrome; avoid concomitant use. | Major |
| Theophylline | Mebendazole may increase theophylline levels; monitor for toxicity. | Moderate |
7. Patient Counselling
- DO complete the full course as prescribed, even if symptoms improve.
- DO take the tablet with a fatty meal if prescribed for systemic infection (like hydatid).
- DO practice strict personal hygiene (handwashing, nail trimming) to prevent reinfection, especially in pinworm.
- DO wash bedding and underwear in hot water for pinworm infection.
- DO NOT take a double dose if you miss one. Take it as soon as remembered, or skip if close to next dose.
- DO NOT take with metronidazole unless advised by your doctor.
8. Toxicology & Storage
Overdose: In acute overdose: Nausea, vomiting, abdominal cramps, diarrhea, dizziness, headache. In chronic high-dose overdose (as in hydatid treatment): Risk of severe hepatotoxicity, agranulocytosis, alopecia.
Storage: Store below 30°C in a cool, dry place. Protect from light and moisture. Keep out of reach of children.