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