dr_singh246
internal medicine pgy2
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please Explain pH dependent urinary drug elimination. the effects of altering ph on elimination of drugs. which drugs are eliminated by alkaline and by acidic ph.
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| mdwannabe
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In order for drug to be permiable to membrane it has to be at neutral charge, coz ionized meds do not easily cross. So, since most drugs, once crossed are in fact neutral, they are excreted to tubules as neutral as well. If you remain urine as is, at time of exretion, the drug that is excreted will be reabsorbed, so one makes urine more acidic or more alkaline, depending on the original drug pKa, to prevent reabsorbtion and increase elimination. Acids are most highly ionised at a high pH, bases are most highly ionised in an acidic environment.
You just need to remember some drugs that are acidic or alkaline. ASA-acidic, Lidocane weak base. etc.
Hope this helps.
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| dr_singh246
internal medicine pgy2
Topics: 235
Posts: 561
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does it means that we r trying to alter urine ph as per the drug we wish to eliminate by making the drug as neutral as possible with respect to urine ph value so that it eliminates.
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| mdwannabe
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no...we make urine pH adjusted so the drug in urine becomes more ionized, to be eliminated.
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| dr_singh246
internal medicine pgy2
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Posts: 561
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ok got it. thanks
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to love when it can be lost, to go on when progress seem futile and to believe in every fiber of your body. to live , have hope and faith and to never give in.... dr_singh246@yahoo.com
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| dr_singh246
internal medicine pgy2
Topics: 235
Posts: 561
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A pharmacologist is determining the pharmacokinetic parameters of a novel antibiotic in order to determine the proper dosage. The drug is a weak organic acid with a pKa of 3.0. Assuming a pH of 2.0 in the stomach, approximately what percent of the drug will be in a form that can be rapidly absorbed from the stomach?
A. 0.1
B. 1
C. 10
D. 50
E. 90
F. 99
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| mdwannabe
Forum Guru
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I think there is a mistake in question...
If you take acidic medication, at pKa it is 50% ionised, if you add 2 pH points, it becomes 90% ionised, if you reduce the pH by two units, it becomes 10% ionised.
In this particular case there is no correct answer. It should become between 90% and 50% available for absorption.
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| dr_singh246
internal medicine pgy2
Topics: 235
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ok lets take second opinion. i m posting the ques as new topic.
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| mdwannabe
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sure :-)
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| krishie
Forum Senior
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Hi,
Ph-pka=-1,hence,90%of acid is in nonionised form.So,since nonionised form is absorbed,it must be 90%.Please correct me if wrong.
Krishie.
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krish
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