topic 15

Question 1

What are 2 classes of nematodes? What nematodes are included in each?

Answer 1

In GI tract

Ascaris lumbricoides (roundworm)
0.8-1 billion

Trichuris trichiura (whipworm)
0.5-0.8 billion

Enterobius vermicularis (pinworm)
Universal

Strongyloides stercoralis (threadworm)
50-100 million

Ancylostoma duodenale and Necator americanus
(hookworms)
20% of population

Cause systemic infection

Trichinella spiralis (trichinosis)-parasite in GI tract and skeletal muscle.

Filariae worms
transmitted through bite of insect vectors

Wuchereria bancrofti (elephantiasis)- parasite in lymph glands

Onchocerca volvulus (river blindness)-parasite located in lymph glands and eye.

Question 2

What 3 drugs are used to treat GI infections caused by nematodes?

Answer 2

Mebendazole, albendazole, pyrantel pomoate

Question 3

What is the mech of action of mebendazole and albendazole?

Answer 3

It inhibits uptake of glucose and uncouples oxidative phosphorylation

In addition, it binds b-tubulin and blocks microtubule polymerization.

The result of the drug effect on the parasite is to cause immobilization, death and expulsion from the G.I. tract

Question 4

What is the absor, admin, of mebendazole?

Answer 4

Mebendazole is poorly absorbed (10-15%) and unabsorbed drug excreted in stool.

Question 5

What is the absorp, admin, distr of albendazole?

Answer 5

Absorption is good when taken with fatty meal.

CNS levels reach 50% of serum levels.

Question 6

What is the spectrum of albendazole?

Answer 6

Specificity: Broad spectrum

T. trichiura, A. duodenale, N. americanus, A. lumbricoides, E. vermicularis infections

Drug of choice for treatment of cysticercosis due
Taenia solium

Question 7

What is the absotp, admin, and mech of action of pyrantel pomoate?

Answer 7

This drug is taken orally and poorly absorbed from the GI tract.

Mechanism of Action
It is a depolarizing neuromuscular blocking agent.
It acts as an agonist causing persistent activation of nicotinic acetylcholine receptors.
This results in worm paralysis and removal by gut peristalsis.

Question 8

What are the side effects of pyrantel pomoate?

Answer 8

If taken in exceptionally large amounts (greater than 1g), enough drug can be absorbed to cause neuromuscular blockade in host.

Question 9

What is the spectrum of pyrantel pomoate?

Answer 9

It is effective in treating infection by A. lumbricoides. N. americanus and A. duodenale.

It is the drug of choice for treating
E. vermicularis infections.

Question 10

Which drugs are used to treat systemic infections caused by nematodes (wuchereria bancrofti)

Answer 10

diethylcarbamazine, Ivermectin

Question 11

What is the absorp, admin, mech of action of diethylcarbamazine?

Answer 11

The drug is given orally and is readily absorbed from the G.I. tract.

Mechanism of Action
** mechanism unknown but may be hyperpolarization of muscle

The drug appears to sensitize filarial worms to phagocytosis by macrophages.

Question 12

What are the side effects of diethylcarbamazine?

Answer 12

More serious is a severe inflammatory reaction to released proteins of the phagocytized filarieae called Mazzotti reaction

Question 13

What is the spectrum of diethylcarbamazine?

Answer 13

Active against filarial infections
Wuchereria bancrofti (given with albendazole)

No longer used for Onchocerca volvulus b/c it caused eye damage.

Question 14

What is the admin, absorp, and mech of action of ivermectin?

Answer 14

Well absorbed, administer on an empty stomach.

Mechanism of Action
Activates GABA and glutamate-gated chloride channels only in invertebrates causing tonic paralysis of muscles.

Question 15

What are the side effects of ivermectin?

Answer 15

Side effects and Precautions
Main side effect is Mazzotti reaction with hypotension, fever, pruritis, bone and joint pain (mild in 10-15% in first time users but can be severe in 5%).

At higher doses or in patients with a damaged brain barrier CNS toxicity can occur as indicated by tremors, ataxia and lethargy.

Question 16

What is the spectrum of ivermectin?

Answer 16

Clinical uses

Effective against W. bancrofti (given with albendazole), O. volvulus and S. stercoralis.

Question 17

What are the different kinds of cestodes (tapeworms) and where are they found in the body? What drug is used to treat them?

Answer 17

Taenia solium (pork tapeworm)-found in GI tract and larvae in tissues (cysticercosis)

GI infections:

Diphyllobothrium latum (fish tape worm)
Taenia saginata (beef tapeworm)
Hymenolepis nana (dwarf tapeworm)

Praziquantel

Question 18

What is the admin, absorp, metab, and mech of action of praziquantel?

Answer 18

80% of oral dose is absorbed and is metabolized by liver p450 enzymes.

Patients with depressed liver function may require adjustment of dosage.

It increases parasite membrane permeability to cations (Ca2+) causing severe muscular contraction.

Praziquantel does not kill cestodes in vivo, but causes the worms to be dislodged from their usual sites of residence in the intestine.

Question 19

What are the side effects of praziquantel?

Answer 19

Both Albendazole and Praziquantel
are contraindicated in patients with ocular cysticercosis (T. solium infection) due to host response that can damage eye.

Question 20

What is the spectrum of praziquantel?

Answer 20

Broad spectrum drug which is effective against all types of tape worms: Taenia solium, Diphyllobothrium latum, Taenia saginata and Hymenolepis nana in the GI tract.

Alternative to treat T. Solium cysticercosis when used at high doses. Albendazole is preferred treatment for cysticercosis

Question 21

Where in the body can trematodes (flukes) be found? What kind of infection do they cause? What are some examples? What is the drug of choice to treat them.

Answer 21

systemic infection

Blood flukes

Schistosoma haematobium is prevalent in Africa,
Schistosoma mansoni -Africa and America
Schistosoma japonicum- far east.

Liver flukes

Clonorchis sinensis- encysted larvae from raw fish

Lung flukes

Paragonimus westermani-encysted larvae in crab meat

Praziquantel