Mebendazole is a worm medicine tablet used to treat the most common intestinal infestations: roundworm, pinworm, hookworm and whipworm. A single dose resolves most cases; it is sometimes repeated after 2 weeks.
Also known as: Vermox, Emverm
Cimetidine inhibits mebendazole metabolism and potentiates its pharmacological effects; the clinical relevance is mainly in prolonged therapy.
Inhibition of hepatic mebendazole metabolism: the Prontuário (Mebendazole 1.4.1) states that "cimetidine inhibits mebendazole metabolism, potentiating its pharmacological effects (these interactions are only clinically significant in prolonged therapy)".
Liver enzymes and full blood count at high or prolonged doses.
Persistent nausea, jaundice, fever, cytopenias.
With single doses (enterobiasis, ascariasis) the risk is minimal; in prolonged therapy (hydatid disease) prefer another antiulcer agent and monitor mebendazole adverse effects.
INFARMED Prontuário Terapêutico (11th ed., 2012), Mebendazole 1.4.1 — cimetidine inhibits mebendazole metabolism.
Carbamazepine lowers mebendazole plasma concentrations through enzyme induction, risking treatment failure in parasitic infections requiring prolonged therapy.
Enzyme induction of mebendazole metabolism: the Prontuário (Mebendazole 1.4.1) states that "co-administration of carbamazepine and phenytoin reduces mebendazole plasma concentrations (enzyme induction)".
Clinical and imaging response of the parasitic disease, liver enzymes.
Persistence or progression of the parasitic infection, new lesions on imaging.
In prolonged therapy (hydatid disease), discuss with a specialist whether a higher dose or an alternative is needed while maintaining the anticonvulsant; do not stop the antiepileptic because of this interaction.
INFARMED Prontuário Terapêutico (11th ed., 2012), Mebendazole 1.4.1 — carbamazepine and phenytoin reduce mebendazole concentrations.
Phenytoin lowers mebendazole plasma concentrations through enzyme induction, risking treatment failure in parasitic infections requiring prolonged therapy.
Enzyme induction of mebendazole metabolism: the Prontuário (Mebendazole 1.4.1) groups carbamazepine and phenytoin as inducers that lower mebendazole concentrations; phenytoin is also a classic CYP3A4 inducer.
Clinical response of the parasitic infection, liver enzymes; phenytoin levels if dosing changes.
Persistence of the parasitic infection, seizures (if phenytoin is poorly adjusted).
In prolonged therapy, discuss with a specialist adjusting the mebendazole dose or using an alternative while maintaining the antiepileptic; monitor the clinical response.
INFARMED Prontuário Terapêutico (11th ed., 2012), Mebendazole 1.4.1 — carbamazepine and phenytoin reduce mebendazole concentrations.
Mebendazole absorption is inherently low and does not require taking with or without food for its luminal effect (intestinal infection).
Take with or without food, always at the same time for routine.
EMC-UK — Mebendazole SmPC 4.2 ("with or without food").
Contraindicated in the 1st trimester of pregnancy; in mass treatment, defer to the 2nd/3rd trimesters.
Defer treatment until after the 1st trimester; contraception during treatment.
Prontuário Terapêutico INFARMED, 1.4.1 (mebendazole — 1st trimester).
Annex 1 records "Avoid due to toxicity in animal studies" (factor CM). Like albendazole, WHO mass-treatment studies showed no increase in malformations, but the label recommends avoidance — especially in the 1st trimester.
Avoid, especially in the 1st trimester; defer treatment if clinically possible.
Annex 2 records that the manufacturer recommends avoiding (l. 42812); mebendazole systemic absorption is low, so the theoretical risk is small — individualised decision.
Prontuário Terapêutico INFARMED — Annex 1: "Mebendazole — Avoid due to toxicity in animal studies" (l. 40907); Annex 2 (l. 42812). EMC-UK (MHRA) — Mebendazole SmPC (Vermox).
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Broad-spectrum luminal anthelmintic against intestinal nematodes; minimal systemic absorption concentrates its action in the GI tract and gives good tolerance in mass deworming programmes.
Inhibits helminthic β-tubulin polymerisation into cytoplasmic microtubules, irreversibly blocking worm glucose uptake and utilisation; cytocidal (not merely paralytic) to the parasite's intestinal cells.
Minimal: 2–10% of the oral dose (wide individual variation), increased by fatty meals — irrelevant for intestinal nematodes but exploitable in tissue infestations. Plasma peak 2–4 h.
Rapidly metabolised to inactive products (ketomebendazole and hydrolysed metabolites) by intestinal and hepatic biotransformation; < 2% excreted unchanged in urine. Carbamazepine/phenytoin may lower plasma levels; cimetidine raises them.
2.5–5.5 h (absorbed fraction); faecal excretion predominates (unabsorbed fraction and biliary metabolites).
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
