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Which of the following parts of digestive tract most likely represents the main site of absorption of the drug?
A 65-year old man suffering from hypertension has been taking hydrochlorothiazide orally, one tablet daily. Hydrochlorothiazide is an acidic drug with a pKa of about 9.



A. Oral mucosa
B. Stomach
C. Small intestine
D. Colon
E. Rectum

This question is part of block 9 pharm drug absorbtion w exp

Asked by Elizabeth, Last updated: Jul 03, 2020

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1 Answer

John Smith

John Smith

Answered Sep 09, 2016

Small intestine-16) learning objective: describe the main features of lipid diffusion of drugs across cellmembranesanswer: call drugs given by oral route are absorbed mainly from the small intestine. this is because of thevery large surface area of the small intestine, which is about 250 square meters and representsabout 80% of the total area of the gastrointestinal tract. hydrochlorothiazide is an acidic drug witha pka of about 9, so it will be more lipid soluble in the stomach (where the ph is less than 2) thanin the small intestine (where the ph is around 7). nevertheless absorption will take place mainly inthe small intestine because of the enormous surface absorptive area.a) when a drug is given by oral route it is swallowed and therefore the oral mucosa does notcontribute to absorption.b, d, e) (see explanation above)
 

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