A 32-year-old man comes to the office due to diarrhea, flatulence, foul-smelling stools, and abdominal cramping. He recently returned home from a hiking trip. A smear of his stool sample is shown below: Which of the following is the drug of choice for this condition?

Question

A 32-year-old man comes to the office due to diarrhea, flatulence, foul-smelling stools, and abdominal cramping.  He recently returned home from a hiking trip.  A smear of his stool sample is shown below:  Which of the following is the drug of choice for this condition?

Quizplus · Accepted Answer

When examined for ova and parasites (stool smear with iodine staining), this patient's stool reveals ellipsoidal cysts with smooth, well-defined walls and 2+ nuclei, consistent with Giardia lamblia. Other classic findings include pear-shaped, flagellated trophozoites. Giardia is the most common enteric parasite in the United States and Canada. When an individual drinks contaminated water from an endemic area without first boiling it, Giardia can colonize the duodenal and jejunal mucosal lining. Hikers and campers are particularly susceptible to infection. Giardiasis causes chronic diarrhea, malabsorption, and flatulence. Metronidazole is an accepted treatment for this protozoan flagellate. This drug can also be used to treat Helicobacter pylori infections, amebiasis, and trichomoniasis. (Choice A) Inflammatory traveler's diarrhea (marked by stool containing blood and mucus) can be treated with ciprofloxacin or another fluoroquinolone. Cysts would not be present. (Choice C) Mebendazole is an anti-helminthic drug that acts on the microtubules of roundworms such as Ancylostoma, Ascaris, and Enterobius. (Choice D) Albendazole is used to treat the tapeworm (cestode) Echinococcus granulosus. Echinococcus does not commonly cause diarrhea, but rather produces cysts in the liver and elsewhere. (Choice E) Loperamide is an opiate antimotility drug that may be prescribed in some cases of traveler's diarrhea where there is no fever or blood in the stool. (Choice F) Clindamycin has activity against anaerobes (eg, Bacteroides fragilis) and has some activity against some strains of staphylocci and streptococci. (Choice G ) Erythromycin can be used in lieu of fluoroquinolones to treat Campylobacter jejuni, as this organism has shown increasing worldwide resistance to fluoroquinolones. Educational objective: Giardia lamblia is the most common enteric parasite in the United States and Canada and is a common cause of diarrhea in campers/hikers. Iodine-stained stool smear classically shows pear-shaped, flagellated trophozoites or ellipsoidal cysts with smooth, well-defined walls and 2+ nuclei. Metronidazole is the treatment of choice.

A 32-Year-Old Man Comes to the Office Due to Diarrhea