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The following message was posted to: PharmPK
Dear All,
Is it possible to tell whether a drug substance is weakly basic or
acidic from its pka value?
Thanks in advance for your attention.
Dr. S. Adebayo
UTECH School of Pharmacy
Kingston 6,
Jamaica.
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The following message was posted to: PharmPK
The best thing to do is look at the chemical structure. pKa and pKb are
based upon ionization, not whether the compound is an acid or base.
Shelly Dunnington R.Ph., Ph.D.
DunningtonShelly.-a-.praintl.com
913-577-2767
16400 College Blvd.
Lenexa, KS 66219
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The following message was posted to: PharmPK
If you take a compound acidic compounds have low pKa values (higher the
acidity lower the pKa value) where as higher the pka value stronger the
basicity of a compound. For graphical demonstration refer to page
115-116 of
Clin Pharmacokinetics book by Rowland and Tozer third edition.
When you know pKa of a drug it gives the idea on extent of ionization
in a
particular pH and extent of absorption also.
Typically pKa of a compound can be determined using potentiometric assay
(refer to Classical Pharm Analysis Books by AG Becket or Ken Connors) an
example on calculating Pka or Pkb can be found in the Text Book Physical
Pharmacy by Alfred Martin Chapter 9). Other reference that can help you
is
Benet LZ, Goyan JE, J. Pharm Sci 54, 1179 and 1165
Hope this helps.
Prasad Tata
Mallinckrodt, Inc.
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Copyright 1995-2010 David W. A. Bourne (david@boomer.org)