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  #1  
Old 06-02-2010
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Drug Site of action of Spironolactone

A 43-year-old male presents to his primary care doctor with complaints of increasing abdominal girth. He has a long history of alcohol abuse and recently stopped drinking. Spironolactone is prescribed to aid the control of the patient’s increasing ascites. Which of the following is the site of action of spironolactone?
(A) Ascending loop of Henle
(B) Collecting duct
(C) Descending loop of Henle
(D) Distal tubule
(E) Proximal tubule
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  #2  
Old 06-02-2010
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B is for bueno (and also the correct answer)
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Old 06-02-2010
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bueno ???? whats that
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Old 06-02-2010
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no answer is not B
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Old 06-02-2010
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Cool B

i also think its B: early collectin ducts!
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Old 06-02-2010
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i think it s D cuz cortical collecting tubule is a distal tubule
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Old 06-02-2010
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(D) is correct. Spironolactone is a competitive aldosterone receptor antagonist. Its site of action is the late distal tubule where it decreases sodium entry into cells and increases potassium excretion, promoting sodium and water loss with preservation of plasma potassium. Spironolactone is especially useful for patients with hepatic failure, as it counteracts the chronic hyperaldosteronism in these patients.
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Old 06-03-2010
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this is really confusing man. in the FA they said that spironolactone's site of action is collecting duct. so distal tubule is collecting duct u say sam? means that DCT is the same as distal tubule? but early DCT is for thiazides.

can someone pls check with FA and tell me what im understanding here. or should i just consider collecting duct as part of distal tubule and answer distal tubule when both choices are available? or perhaps, just perhaps, the answer to this question may be wrong?
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Old 06-03-2010
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Yes ... " D " is answer ... Distal Convoluted Tubule
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Old 06-03-2010
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Quote:
Originally Posted by Seetal View Post
this is really confusing man. in the FA they said that spironolactone's site of action is collecting duct. so distal tubule is collecting duct u say sam? means that DCT is the same as distal tubule? but early DCT is for thiazides.

can someone pls check with FA and tell me what im understanding here. or should i just consider collecting duct as part of distal tubule and answer distal tubule when both choices are available? or perhaps, just perhaps, the answer to this question may be wrong?
the cortical collecting tubule is a part of the collecting duct system that consists of connecting tubules, cortical collecting ducts, and medullary collecting ducts and duct of Bellini.the spironolactone acts only on the distal tubule(collecting duct tubule) but not the entire collecting duct.So D is the best answer
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  #11  
Old 06-03-2010
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@sheetal i knoe its confusing i just copied the answer they gave

i m really confused to

seniors plzz help with this concept
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Old 06-03-2010
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Quote:
Originally Posted by ecgram View Post
A 43-year-old male presents to his primary care doctor with complaints of increasing abdominal girth. He has a long history of alcohol abuse and recently stopped drinking. Spironolactone is prescribed to aid the control of the patientís increasing ascites. Which of the following is the site of action of spironolactone?
(A) Ascending loop of Henle
(B) Collecting duct
(C) Descending loop of Henle
(D) Distal tubule
(E) Proximal tubule


The answer is "D".

You have to watch out for language. The people that said "B" probably didn't read as slowly as they should have. The Collecting DUCT is lower in the kidney, it regulates mannitol and ADH antagonsists.

The Collecting TUBULE/ Distal TUBULE is where Potassium sparing drugs work.

The best way to answer these questions is to draw out the kidney and mark where each drug works. Don't be fooled by language. The USMLE will trick you with these types of questions you just posted. Before you look at the answer, know in your head you should be looking for something with TUBULE. They can get you every time just by interchanging words on you.

1- Acetazolamide- Proximal
2- Mannitol- Proximal
3- Loops- Thick Ascending
4- Thiazides- Early Distal
5- Potassium Sparking- Late distal tubule / Collecting Tubule
6- ADH antagonists- Collecting DUCT
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Old 06-04-2010
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Okay I am really confused. I think the word DUCT and TUBULES can be used interchangably in the context of collecting tubules/ducts
If you check katzung's pharm under diuretics (ch. 15) ... it has subheadings for each portion of nephron and the major drugs that act on them. It has DCT as its own heading which only mentions the thaizides and under cortical collecting tubule heading, it talks about the portion of the aldosterone receptors and it further goes on to talk about the medullary collecting tubule which posseses ADH receptors.
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