Pharmacology of GI Infections: Abx and Anti-parasite Drugs Flashcards
(46 cards)
Antimicrobial agents that may induce C.diff diarrhea and colitis
Frequently associated drugs include:
Fluoroquinolones
Clindamycin
Cephalosporins (broad-spectrum)
Penicillins
[macrolides and TMX are occasionally associated; rarely associated are aminoglycosides, tetracylcines, metronidazole, and vancomycin
_____ is the preferred pharmacologic tx for severe C.diff infection
_____ is the equivalent which is utilized in mild C.diff infection, sometimes chosen if oral administration won’t work for the pt
Vancomycin; metronidazole
_____ is the agent of choice for recurrent C.diff infection because it spares many anaerobic colonic flora
Fidaxomicin (macrolide family)
Key drugs in tx of H.pylori
Omeprazole (PPI)
Metronidazole
Tetracycline
Bismuth subsalicylate
The therapeutic goals of entamoeba histolytica tx are to eliminate the invading trophozoites and eradicate intestinal carriage of the organism (luminal amebicides); what drugs are utilized to accomplish these goals?
To eliminate the invading trophozoites: metronidazole (drug of choice) or tinidazole (better tolerated)
Eradicate intestinal carriage of the organism: paromomycin or iodoquinol
Both metronidazole and tinidazole must be given with a luminal amebicide to ensure eradication of E.histolytica!
Asymptomatic carriers of entamoeba histolytica have cysts or trophozoites without internalized RBCs. How are these pts treated?
With luminal amebicide agents — paromomycin or iodoquinol
Iodoquinol is used as a luminal amebicide, it has no effect against extraintestinal organisms. It is a halogenated hydroxyquinoline with an unknown MOA.
What is unique about its pharmacokinetics and what are some adverse effects?
90% of the drug is retained in the intestine and excreted in feces
AEs = diarrhea, anorexia, N/V, abdominal pain, HA, rash, pruritis
What clinical feature differentiates G.lamblia from E.histolytica?
No blood in stool (no invasion of intestinal wall)
Pharmacologic agents utilized in G.lamblia
Tinidazole (first-line agent)
Nitazoxanide
Metronidazole (not FDA approved for this but sometimes used)
MOA of nitazoxanide
Inhibition of pyruvate-ferredoxin oxidoreductase enzyme (essential to anaerobic energy metab)
[prodrug of tizoxanide]
Adverse effects of nitazoxanide
Nausea, anorexia, flatulence, increased appetite, enlarged salivary glands, yellow eyes, dysuria, bright yellow urine
Cryptosporidium parvum tx
Antidiarrheal agents: loperamide
Antimicrobial agents: nitazoxanide (preferred) or paromomycin
Fluid management
How does cryptosporidium parvum tx change depending on immune status?
The main goal in an immunocompromised pt is to restore immune function
HIV: antiretroviral therapy may need to be reduced, add nitazoxanide if needed
Other: reduce dose of immunosuppressant + nitazoxanide
How does infection with necator americanus and ancyclostoma duodenale initially begin? What are some clinical features?
Penetration of skin between toes — results in intense itching at site of penetration
Other effects: diarrhea, abdominal pain, weight loss, anemia
How does infection with ascaris lumbricoides initially begin? What are some clinical features?
Consumption of eggs in contaminated food
Clinical features = abdominal cramping, malnutrition, worm invasion
Most helminth infections are diagnosed by presence of eggs in stool. How is Strongyloides stercoralis diagnosed?
Since Strongyloides eggs are not passed in the stool, it is diagnosed by larvae in feces or by enterotest
How is strongyloides stercoralis infection started? What are some clinical features?
Larvae in soil penetrate human skin and travel to lungs —> coughed up and swallowed
Mature worms form in small intestine and release eggs
Clinical features: vomiting, abdominal bloating, diarrhea, anemia, weight loss
Why must you always check for strongyloides stercoralis in asthmatic patients when in endemic areas?
Patients with asthma may be on prednisone, which has immunosuppressive action that can lead to severe autoinfection with Strongyloides stercoralis
What is unique about the lifecycle of trichuris trichiuria (whipworm)?
No larvae, no transit through intestinal wall, no lung involvement, no eosinophilia, no autoinfection
Simple life cycle with ingestion of food with infective eggs
Diagnostic feature of trichuris trichiura
Football shaped eggs seen in feces
Life cycle and features of enterobius vermicularis (pinworm) infection
Eggs ingested, pinworms mature in cecum and ascending large intestine
Female migrates to perianal area to lay eggs —> severe perianal itching and potential for hand to mouth transmission
Dx by scotch tape test; do not cause eosinophilia
Drugs in general used to treat nematode infections
Albendazole Mebendazole Ivermectin Thiabendazole Pyrantel pamoate
MOA of albendazole and mebendazole
Inhibition of microtubule synthesis —> paralyzes worms which are then passed stool
Prodrug is turned into active metabolite after first pass effect
The MOA of thiabendazole is the same as albendazole and mebendazole, but what is different about this drug?
Rapidly absorbed after ingestion, largely excreted in urine, and can be absorbed from the skin
MUCH MORE TOXIC than albendazole and mebendazole —> dizziness, anorexia, nausea, vomiting
Less common effects include irreversible liver failure and fatal Stevens-Johnson syndrome
