A patient had an overdose of aspirin pKa= 3.5 and another withcocaine pKa=9.0. p

Question

A patient had an overdose of aspirin pKa= 3.5 and another withcocaine pKa=9.0. pH of urine is 5-6 . Which will get more absorbedthrough the lipid membrane at pH=2.0 and pH=9.0? the professor saidit has to do with this formula pH=pKa + log [A-]/[HA] Thanks A patient had an overdose of aspirin pKa= 3.5 and another withcocaine pKa=9.0. pH of urine is 5-6 . Which will get more absorbedthrough the lipid membrane at pH=2.0 and pH=9.0? the professor saidit has to do with this formula pH=pKa + log [A-]/[HA] Thanks

Explanation / Answer

The pKa value determines the pH that the compound loses itsproton For better absorption, the compound must be in the protonatedform. Using pH=pKa + log [A-]/[HA] , you can calculate that at pH 2,aspirin is mostly in the protonated form, while cocaine is mostlyin the deprotonated form. Thus, aspirin will get more absorbedthrough the lipid membrane. At pH 9, Aspirin is mostly in the deprotonated form, whilecocaine is halfly protonated and halfly deprotonated. Thus, cocaineis better absorbed at pH 9 Hope this helps!

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