Antiparasitics: antihelminthic drugs Flashcards
Helminth infections - worms have a unique biology. Why?
They multiply outside of their definitive host in contrast to other parasites
They evade the immune system - infections are chronic (last for lifetime of host)
Flatworms aka
tapeworms
Taenia saginata (beef tapeworms) are transmitted by
eating undercooked meat
Taenia solum (pork tapeworms) are transmitted by? what organ do they affect?
eating undercooked pork
affects bladder
Diphyllobothrium latum (fish tapeworm) is transmitted by? what do they do to the host?
eating undercooked fish
they rob the host of nutrients, especially vitamin B12
cysticerosis
- caused by?
- how do they cause infection?
caused by auto infection by ingesting the eggs produced by T. solum
after ingestion, oncospheres hatch in the intestine, invade the intestinal wall, and migrate to striated mm (and brain, liver, and other tissues). Develop into cysticerci. Can cause serious infection in the brain.
dwarf tapeworm (hymenolepis nana)
- special b/c its the ..
- who does it mainly affect?
most common cestode infection
mainly affects children
What are the three species of schistosomiasis (bloodflukes)?
What causes the symptoms we see?
Schistosoma hematobium
Schistosoma mansoni
Schistosoma japonicum
symptoms are cause by immune reactions to the eggs
What drug is used to treat cestodes and trematodes?
Praziquantel
What is the mechanisms of action of praziquantel?
- disrupts Ca homeostatsis
- causes mm contraction followed by spastic paralysis
- immune response likely involved
- worms dislodge and die
Praziquantel is the drug of choice for
all forms of schistosomiasis
What problems do we see with praziquantel treatments?
- severe immune reaction to the worm after it has been killed
- increased abortion rates in rats - so avoid if prego
- may cause dizziness/drowsiness - avoid driving
Hookworms are found where?
How do we become affected with them?
What do they feed on?
What are the consequences of hookworm infections?
Found in soil
They can penetrate the skin or can be orally digested
They feed on intestinal tissue and blood
Cause
- pulmonary lesions
- skin reactions
- intestinal ulceration
- anemia
Enterobiasis - life cycle?
- Live in GI tract
- Female migrate to rectum at night to deposit eggs
- Causes perianal pruritis
- Eggs infect fingers and bed sheets (remain infective for 3 weeks)
- Ingesting of eggs starts new infection cycle
Ascariasis aka
roundworms
Ascariasis - life cycle?
- Eggs are ingested
- larva hatch in small intestine
- penetrate intestinal wall and are transported to lungs
- after ~ 10 days, pass out through lungs to trachea and are re-swallowed
- return to small intestine
Whipworm infections (trichuriasis)
- caused by ..?
- causes (effects of infection)..?
Caused by ingesting eggs in contemned food or liquids
Causes irritation and inflammation of colonic mucosa, abdominal pain, diarrhea, and distention
Trichinosis
- associated with ..?
- causes ..?
associated with undercooked pork
causes diarrhea, abd pain, nausea and mm pain, edema, and weakness
Filariasis
- where in the body do we find it?
- what does it cause?
its lymphatic dwelling
causes elephantiasis
eyeworm (loa loa)
transmitted by deed flies
ocular lesions can cause blindness
river blindness (onchocerca volvulus)
transmitted by female blackflies
causes blindness?
Benzimidazoles mechanism of action
- bind to tubulin
- inhibit formation of microtubules
- can bind to mammalian tubulin
Pharmacokinetics of benzimidazoles
- poorly absorbed in GI - eating a fatty meal increases absorption
- – can take advantage of this - if infection in intestine, take on empty stomach; if infection in tissue, take with fatty meal to increase absorption
-rapidly metabolized in the liver
Toxcity of thiabendazole
- side effects?
- should not be used when?
- dizziness, anorexia, nausea, vomiting
- should not be used in pregnant women
mebendaolze is …?
teratogenic
-not used in pregnant women
Therapeutic uses of albendazole
drug of choice for cysticercosis
also used for pinworms, hookworms, ascarasos, trichuriasis, and strongyloidiasis
Therpeutic uses of mebendazole
used for pinworms, hookworms, ascariasis, and trichuriasis
Diethylcarbamazine is the drug of choice for …?
What adverse effects do we see with treatment here?
Filariasis and loiasis
Dying worms can cause severe infection
— may lead to systemic inflammation from release of bacterial endosymbiont
Ivermectin is the drug of choice for?
Strongyloidiasis and onchocerciasis
Ivermectin mechanism of action?
- paralyzes microfilariae
- intensifies GABA mediated transmission of signals in peripheral nerves
- allows host cytotoxic cells to adhere
- does not kill adult worm; blocks release of progeny
Ivermectin therapeutic uses?
- primarily used to treat onchocerciasis
- single dose
Pyrantel pamoate is a
- bioavailability?
- effective against?
broad-spectrum antihelminth that is available over the counter
bioavailability is very low
highly effective against pinworms and ascaris; moderately effective against hookworm
Pyrantel pamoate mechanism of action?
neuromuscular blocking agent
causes release of Ach and inhibition of cholinesterase
worms are paralyzed and expelled
How do we treat trichinosis?
mebendazole + coritcosteroids
How do we treat strongyloidiasis?
mebendazole or albendazole
How do we treat onchocericiasis
ivermectin
How do we treat filariasis?
diethylcarbamazine
Most important human parasitic helminth infections can be treated with one of the following drugs
- diethylcarbamazine
- ivermectine
- mebendazole or albendazole
- praziquantel
- pyrantel pamoate
