Anthelmintics
Content
Anthelmintics
• Classification
• Pharmacology
At the end of this lecture, the student will be able to:
• Classify anthelmintic drugs
• Describe the pharmacology of Anthelmintics
Anthelmintics
• Anthelmintics are drugs that either kill (vermicide) or expel (vermifuge) infesting helminths
Chemotherapy for helminthic infection
• Broad spectrum Anthelmintics – Benzimidazole group
– Thiabendazole
– Mebendazole
– Albendazole
– Triclabendazole
• Against Nematodes
– Pyrantel pamoate
– Levamisole
– Piperazine
– Diethyl carbamazine
– Ivermectin
– Thiabendazole
– Doxycycline
• Against Trematodes
– Metrifonate
– Oxamniquine
– Bithionol
– Triclabendazole
• Against Cestodes
– Niclosamide
• Against Trematodes + Cestodes
– Praziquantel
Benzimidazoles
• Broad spectrum anthelmintics
• Binds to β-tubulin filaments of helminths
• Prevents polymerisation leading to breakdown of cytoplasmic microtubules
• Selective and irreversible inhibition of glucose uptake
• Depletion of parasitic glycogen storage
• Reduced formation of ATP and disrupted metabolic pathway
• Parasitic death
Albendazole
Broad spectrum oral anthelmintic
Pharmacokinetics
• Variable oral absorption
• Fatty meal increases absorption by 5 folds
• Metabolised in liver to active sulfoxide metabolite
• Distribution - Bile, CSF and hydatid cysts
• Elimination half-life – 8-12 h
Clinical Uses of Albendazole
• Effective against intestinal nematodes, cestodes and liver fluke
• Drug of choice for round worm, whip worm, hook worm
• Dose – Adult and children above 2 yrs – 400 mg single dose at night
– Children 1-2 yrs – 200 mg OD
For heavy worm infestation – dose repeated 3 days
• Alternative drug for the treatment of
– Strongyloides stercoralis (thread worm) – 400 mg OD for 3 days
– Enterobius vermicularis (pin worm) – 400 mg OD to be repeated after 2 weeks
• Synergistic combination with diethyl carbamazine or ivermectin for treating or controlling lymphatic filariasis
Adverse effects of Albendazole
• Well tolerated
• Side effects are rare for a short period
• If used for 3 months
– Epigastric distress
– Headache
– Alopecia
– Fatigue
– Insomnia
• Teratogenic in animals, long term use in pregnancy is avoided
Mebendazole
• Prototype benzimidazole with wide spectrum anthelmintic activity
Pharmacokinetics
• Oral absorption is erratic (10%)
• Absorption is increased with fatty meal
• Metabolised to decarboxylated metabolite in liver
• Excretion – Urine, little amount in bile
• Half-life – 2-6 h
Clinical Uses of Mebendazole
• For treatment of round worm, hook-worm and Whip-worm infestation
• Dose – 100 mg BD for 3 days
• 95-100% cure rate in pin worm infestation
• Used for mixed infections (ascaris + hook worm or ascaris + hook worm + whip worm)
• Alternative drug for the treatment of intestinal capillariasis, visceral larva migrans and Taenia saginata
Adverse effects of Mebendazole
• Abdominal discomfort , nausea, vomiting & diarrhoea
• Higher doses – Rash, Urticaria, elevated aminotransferase
• CI in liver cirrhosis
• Teratogenic in few animal species
• CI in pregnancy
Summary
• Anthelmintics are drugs that either kill (vermicide) or expel (vermifuge) infesting helminths
• Classified based on their action against different helminths
• Benzimidazole derivatives are broad spectrum anthelmintics used against nematodes, cestodes and trematodes
• Other drugs include pyrantel pamoate, piperazine, diethyl carbamazine, piperazine, niclosamide, praziquantel
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