Lecture 9 Antihelmintics

Question 1

What are the different classifications of helminths?

Answer 1

Intestinal nematodes (roundworm, hookworm, tapeworm)
Tissue nematodes (Filaria)
Platyhelminths (trematodes and cestodes)

Question 2

Which is the only gut helminth that can multiply in the host?

Answer 2

Strongyloides stercoralis.

Question 3

What is cysticercosis?

Answer 3

Infection by a parasite called Taenia solium, a pork tapeworm that creates cysts in different areas in the body.

Question 4

Why are most anthelmintics selectively toxic?

Answer 4

They target the nervous system in helminths which has important differences from the nervous system of vertebrates.

Question 5

What sort of infection is Schistosomiasis? how and Where can infection occur ?

Answer 5

Schistosomiasis is an infection with flukes of the genus Schistosoma. S haemotobium affects the bladder and urinary tract. S mansion affects the intestine.

Question 6

What is pork tapeworm treated with?

Answer 6

praziquantel.

Question 7

What is Trichuris trichiura? Which disease does it cause, and how can it be treated?

Answer 7

Whipworm. Causes lymphatic filariasis (elephantiasis) and can be treated with mebendazole.

Question 8

What helminths can mebendazole be used to treat?

Answer 8

Threadworm, Acaris lumbricoides, hookworm, whipworm.

Question 9

What is the MOA of ivermectin?

Answer 9

It is effective against most nematodes (round worms) and enhances GABA-mediated inhibition at the neuromuscular junction, causing flaccid paralysis of the worms. Also activates a glutamate-gated chloride channel found only in invertebrates.

Question 10

Which worms are GABAergic drugs ineffective against? Why?

Answer 10

Innefective against trematodes (flukes) and cestodes (flatworms) because they do not have peripheral GABAergic nerves.

Question 11

What is the MOA of praziquantel?

Answer 11

Induces muscular contraction and spastic paralysis by increasing calcium fluxes (increases permeability to calcium). Effective in schistosomiasis.

Question 12

What is the MOA of mebendazole?

Answer 12

Binds to beta-tubulin in nematode cells to inhibit microtubule polymerisation. The transport of secretory granules and other organelles is blocked.

Question 13

Describe the use of albendazole.

Answer 13

Predominantly used to treat intestinal worm infections such as Ascaris lumbricoides (roundworm), Enterobius vermicularis (threadworm), hookworm and whipworm.
Used as adjunctive therapy for hydatid disease, and used for the treatment of cutaneous larva migraines as an alternative to ivermectin and should be taken with a fatty meal for this indication.

Question 14

What are the main adverse effects of Albendazole and mebendazole?

Answer 14

Raised transaminases, gastrointestinal upset and haematological abnormalities.

Question 15

What are the practice points for albendazole and mebendazole?

Answer 15

Avoid albendazole in pregnancy and children under 6 months.
For systemic infections, take with a fatty meal to improve absorption. For intestinal worms, should be taken on an empty stomach to limit absorption.

Question 16

What worm is triclabendazole used for?

Answer 16

Treatment of Fasciola hepatica (liver fluke).

Question 17

What is ivermectin used to treat?

Answer 17

Filariasis, onchocerciasis (river blindness spread by black flies), strongyloidiasis, crusted scabies, head lice and cutaneous larva migraines.

Question 18

What is the contraindication for ivermectin, and describe the sensitivity to the drug.

Answer 18

Contraindicated in pregnancy and not recommended for use in children under 5 years.
Sensitivity in filarial infections arise from the drug’s effect on microfilariae, but are usually transient and respond to analgesics and antihistamines. Best taken with fatty meal.

Question 19

Describe the use of prizaquantel, and its transient adverse effects.

Answer 19

Used predominantly for schistosomiasis. May be used as adjunctive therapy for hydatid disease.
Adverse effects include GI upset, headache, dizziness and drowsiness.

Question 20

Describe hydatid tapeworm disease.

Answer 20

Commonly infects dogs. Person may contract it from infected dog poo, and cysts form in vital organs such as the liver, lungs and brain. Treatment: albendazole, surgery, cyst aspiration or instillation of scolicidal agents.

Question 21

What is pyrantel used for? How does it work?

Answer 21

Effective against Roundworm, hookworm and threadworm. Causes spastic paralysis of worms by acting as a depolarising neuromuscular blocking agent. This results in worm detachment and expulsion from GIT.