NS FL5 Physical Sciences Q33

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NS FL5 Physical Sciences Q33

Post by avo » Mon Jul 15, 2019 5:20 am

For this question, I was able to get the question right and identified that A/D were the right answer, and also noticed the correct answer also correlating with the carbonic acid buffer. That said, I wasn't entirely able to understand why the answer had to be a base and couldn't be acidic if all we had to do was make the drug charged to prevent absorption?
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Re: NS FL5 Physical Sciences Q33

Post by NS_Tutor_Mathias » Tue Jul 16, 2019 2:42 pm

You wanted to make it CHARGED, so you wanted to bring the blood pH further away from the pKa of the drug, so that a greater fraction of it would be ionized. Administering a base to the patient will increase their blood pH, and in turn leave more Tolbutamide ionized and therefore able to be excreted rapidly.

The key concept here is that of ionization of chemical species at different pH, which actually doesn't have that much to do with buffering. The use of sodium bicarbonate is because we only want to shift the pH of the blood slightly, within the bounds of the tolerable. More radically altering a patient's internal chemical environment is generally frowned upon as it will lead to a very poor outcome and felony charges.
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