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Skip to 0 minutes and 10 seconds How about general question number two Drug B is greater than 90 percent excreted unchanged in the urine if the drug is administered to a renal insufficient patient with a GFR of 30 and which drug regimen is the best choice? Here we can apply the method of estimation in other words to eliminate it eliminate this wrong answers first. So let’s look at B those should be increased due to decrease renal excretion no drug should be increased because of decrease the organ function really, so B is wrong. Standard dosing schedule C is in patient as in the patient with normal kidney function.

Skip to 1 minute and 7 seconds Well since the drug is greater than 80 percent excreted unchanced so we do have to do something about dosing regimen in renal failure. So C is incorrect. D patients should not receive drug B and this type of choice is really a distractor it’s we call it red herring that is a nonsense option So the correct answer is A. Dose should be decreased due to decreased renal function Question number three Drug C is 99% excreted unchanged in the urine in renal failure the half-life increases and the clearance decreases but volume of distribution remains the same. So if a patient develops develops severe renal failure, what is your best choice for those in drugs C?

Skip to 2 minutes and 12 seconds Here please pay attention to the key phrase that is the volume distribution remain unchanged So with that in mind, let’s review the options First, loading those should decrease Second, B, loading those should decrease Now we know the definition of loading dose printed in red is equal to volume distribution times steady-state concentration or therapeutic concentration since the volume distribution stays the same so loading dose should really stay the same So A and a B are out.

Skip to 2 minutes and 57 seconds So leaving C and the D Let’s look at D Loading dose should stay the same and the dosing interval should also stays the same this doesn’t appear to be correct In fact C is correct Loading does should stay the same but the dosing interval should increase or should be prolonged or the drug should not be given as frequent. Question number four, in patient with chronic renal disease which biological factor is most likely to alter a drug’s volume of distribution This one you kind of just to sort of memorize it because the primary effect of renal failure is the

Skip to 3 minutes and 53 seconds change in volume of distribution00:03:55.680 –> 00:04:01.000 and that is due to the reduced plasma protein binding

Skip to 4 minutes and 1 second in chronic renal failure and again that’s due to the competition of protein binding of the drug with the uremic toxin or was the accumulated fatty acid So C is the correct answer It’s the altered plasma protein binding.

General questions 2-4 : Drug regimen and protein binding

Continuing from the previous step, Prof. Lee illustrates 3 general questions this time.

For the second general question, it is obvious that we should decrease the dosage since the patient’s estimated GFR is only 30 mL/min.

For the third one, the key is that the volume of distribution (V) remains unchanged.

Do you still remember how to calculate the loading dose? It is the product of V and steady-state concentration. Therefore, due to the unchanged V, it is clear that loading dose should stay the same as well. When a patient’s renal function is damaged severely, we should prolong the dosing interval for sure.

For the fourth question, we should keep in mind that the protein binding for the drug is most likely to affect a drug’s volume of distribution.

If you have any questions or thoughts, please do not hesitate to leave them below.

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This video is from the free online course:

Pharmacokinetics: Drug Dosing in Renal Disease

Taipei Medical University