A subject in whom the inulin clearance is 120ml/min, is administered a,drug whose clearance is 18ml/min. If drug is 40% plasma protein bound then what percentage of Filtered drug must be reabsorbed in the renal tubules?
GFR = 120 ml/min so 120 ml/min of plasma is being cleared from some substance by the kidneys. Protein-bound substances are NOT filtered so only 60% of that 120 ml of plasma contating that drug will be filtered, so 120 ml/min x .06 = 72 ml/min - and that's in theory.
BUT...
In practice we know from the stem that only 18ml/min is being cleared from that drug. So it means that some fraction of drug has been reabsorbed in the tubules.
so now we see that 72 ml/min has been cleared at the level of glomerulus but only 18 ml/min was actually cleared at the end of the tubule journey 72 - 18 = 54 - that's the amount that has been reabsorbed. so now we calculate what fraction of initially cleared plasma is the reabsorbed amount.
54/72 = 75%.
so E) is the answer here.
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
USMLE Forums
402.5K posts
115.2K members
Since 2009
A forum community dedicated to the United States Medical Licensing Examination. Come join the discussion about schools, exams, news, prep, reviews, accessories, classifieds, and more!