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  #1  
Old 02-09-2012
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Drug Weak base drug pharmacokinetics!

Pilocarpine is being considered for the treatment of Glaucoma in 58 year old patient. Except for elevated intraocular pressure, the patient's history and physical exam are unremarkable. Pilocarpine is a weak base of Pka 6.9. Which of the following statement is false??

A) after parenteral administration, the concentration of pilocarpine in the aqueous humor(PH-7.8) will be lower than the concentration in the duodenum(PH-5.5)
B) When administered as eye drop, absorption into the eye will be faster if the drops are alkaline (PH-8.0) than if they are acidic(PH-5.5)
C) Excretion in the urine will be faster if urine PH is alkaline (PH-8.0) than if the urine PH is acidic (PH-5.8)
D) The proportion of pilocarpine in the protonated form will be approximately 90% at PH-5.9
E) The proportion of pilocarpine in the more lipid soluble form will be approximately 99% at PH-8.9


It would be better if you put down the explanation that why you choose the option
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  #2  
Old 02-09-2012
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Default

Ans B ..... becoz ph of aqueous ph is slightly acidic of 7.2 so weak bases would be easily absorbed .....
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Old 02-10-2012
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Default i think its C

pilocarpine being a weak base will ionize in acidic urine and will be excreted faster than in alkaline urine (if im not mistaken,its been a while since i did pharma and i hate pharmacokin/dyn!)
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  #4  
Old 02-10-2012
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Smile Answer is here

Weak bases are more protonated in an acidic enviornment because more prtons are available.In the protonated state,weak bases are ionized,polar and less lipid soluble.Therefore less pilocarpineis lipid solubleand able to diffuse through the duodenum(PH-5.5) than is able to diffuse through the surface of the eye(PH-7.8). By the same reasoning,the drug diffuses faster if the eye drops are alkaline than if they are acidic.Less drug diffuses back into the body from the urine if urine PH is acidicthan if it is alkaline,so excretion will be faster in acidic urine
So correct answer is definitely C
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Old 02-11-2012
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Default Great explanation

b/c I did NOT think it was C. Thanks
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