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Calculating acids,absorption and antibiotics?

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Calculating acids,absorption and antibiotics?

Postby piloting » Thu Mar 15, 2012 3:04 pm

There's a new antibiotic developed for oral admin

It has a pH=2 (stomach) , pH=6 in the intestine and pKa=2.1

a)Will the drug dissociate in aqueous soln's as a weak or strong acid?

b)Calculate the drug amount dissociated as % ionized and % non-ionized for each body part

c)Will the compound be absorbed by passive diffusion better in the intestines or stomach?

Here are some equations that'll help

pH=pKa+log[A-/HA]

Ka=[H+]*[A-]/[HA]

%[A-] ionized = ([A-]/[HA]+[A-]) * 100

%[HA-] non-ionized = ([HA-]/[HA]+[A-]) * 100

HA[two arrows pointing in opposite directions]A− + H+

pKa=-log10Ka

These questions have been a real stumper for lots of people in my class
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Re: Calculating acids,absorption and antibiotics?

Postby Darby » Sun Mar 18, 2012 2:43 pm

Do the environmental pH's (stomach and intestine) have to be factored in? I'm not sure, just asking.
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Re: Calculating acids,absorption and antibiotics?

Postby piloting » Sun Mar 18, 2012 11:19 pm

Darby wrote:Do the environmental pH's (stomach and intestine) have to be factored in? I'm not sure, just asking.


Yes
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Postby JackBean » Mon Mar 19, 2012 2:05 pm

there is nothing like HA-! It's either A- or HA, as you have it in your equation HA = A- + H+

a) look up definitions of weak and strong acids.
b) all you need is pH=pKa+log[A-/HA] :roll:
c) which form (HA or A-) will be in stomach and which form will be in intestine? Which of these forms will difuse more easily through the plasma mebrane?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
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