Antiparasitics Flashcards
What are the most common parasitic infections in the US?
What factors can make one high-risk for these infections?
Toxocara > Giardia > Amebiasis > Trichomonas > Helminth
Many parasites are diseases of the poor–higher incidence in inner city people and those of ethnic minorities.
What are some unique considerations in designing antiparasitic therapies?
They are often eukaryotes and may not have significantly different biochemistries from the host. Toxicity is a greater concern.
Often, treatment requires eliminating the parasite in several different life stages (eg Cestodes and their eggs).
Name some roundworm infections.
Describe the typical roundworm life cycle.
What are some treatments for roundworm infections?
Ascaris, Strongyloides, roundworms, pinworms, hookworms, whipworms, trichinosis, filariasis…
Most roundworms have a rhabditiform and filariform larval stage; the latter penetrates the host’s skin. Some may move to the lungs to be coughed up and swallowed. Fecal excretion of eggs or worm.
Mebendazole, Albendazole, Thiabendazole, and Pyrantal pamoate.
Mebendazole
What is its mechanism of action?
What are its indications?
What are its side effects?
Mebendazole
Immobilizes and kills parasites (interferes with microtubules).
Used in roundworm infections–also can kill the ova.
Few side effects, thanks to its poor absorption (oral, only needs to work lumenally)
Albendazole
What is its mechanism of action?
What are its indications?
What are its side effects?
Albendazole
Like mebendazole; damages microtubules.
For echinococcus and treatment of roundworms that cause larva migrans. Also used to treat cestodal infections.
Because it is well-distributed, it may cause N/V, headache, abdominal pain and elevation of hepatic enzymes.
Thiabendazole
What is its mechanism of actions?
What are its indications?
What are its side effects?
Thiabendazole
Interferes with microtubules, and inhibits energy metabolism.
For strongyloides and other roundworms that can cause larva migrans. For pets, too.
It is rapidly absorbed, and associated with N/V and dizziness.
Pyrantel Pamoate
What is its mechanism of actions?
What are its indications?
What are its side effects?
Pyrantel Pamoate
It is a depolarizing neuromuscular blocker.
It has a relatively narrow spectrum of use; for hookworm/pinworm/roundworm (but not whipworm!). Available OTC.
Since it is poorly absorbed, it has only mild GI symptoms.
Praziquantel
What is its mechanism of action?
What are its indications?
What are its side effects?
Praziquantel
Increases calcium permeability, causing spastic paralysis (in the parasite).
used to treat fluke infections such as Shistosoma and other trematodes. Also used in cestodal infections.
Some abdominal discomfort and nausea.
Name some cestodal infections.
Describe the cestodal life cycle.
What are some treatments for cestodal infections?
Taenia Solium/Saginata, Diphyllobothrium Latum, Echinococcus, and Hymenolepsis.
Larvae encyst in the meat of pigs, cows, fish or other animals. Upon ingestion by a human, mature and attach to the GI tract. If eggs are ingested (fecal-oral), cysts may implant in the human (brain = neurocysticercosis).
Praziquantel, Albendazole, Paromomycin Sulfate.
What useful trait does praziquantel have with respect to tapeworm infections?
What is albendazole used to treat, asides from roundworm infections?
When is paromomycin sulfate indicated?
It can kill the ova of Taenia Solium.
It is a first-line agent for neurocysticercosis.
It is a third-choice, for those who can’t tolerate praziquantel or albendazole.
What are some special considerations in treating malaria?
There is currently no way to kill the sporozoites (ie no way to stop initial infection). Treatment usually focuses on taking out the blood schizonts, but P. Vivax and P. Ovale leave liver schizonts.
Chloroquine
What is its mechanism of action?
What are its indications?
What are its side effects?
Chloroquine
It concentrates in the acidic vacuoles of infected erythrocytes by ion trapping, where it inhibits heme metabolism.
It is a blood schizonticide for treatment and prevention of all 4 species of malaria.
Well-tolerated; some visual impairment with long-term use.
Mefloquine
What is its mechanism of action?
What are its indications?
What are its side effects?
Mefloquine
Same as chloroquine; block heme metabolism.
It is a blood schizonticide for treatment and prophylaxis against chloroquine-resistant P. Falciparum/Vivax.
It can cause vestibular (dizziness/vertigo) and psychiatric (anxiety/paranoia/depression) disturbances. It is contraindicated in patients with psychiatric disorders or epilepsy.
Atovaquone
What is its mechanism of action?
What are its indications?
What drug is it often administered with?
Atovaquone
it is a ubiquinone analog and blocks bacterial electron transport (cytochrome bc1) to block pyrimidine synthesis.
Used as a blood schizontocide. against resistant P. Falciparum when combined with proguanil.
Proguanil. (“Malarone”)
Proguanil
What is its mechanism of action?
What are its indications?
What are its side effects when combined with atovaquone?
Proguanil
Following prodrug activation by CYP2C9, it inhibits DHF reductase (like TMP) to block pyrimidine synthesis.
It is is a blood schizontocide against resistant *P. Falciparum *when combined with atovaquone.
The combination is wel tolerated, but there is some N/V/D, rash, headache.
