The polar surface area (PSA) of a molecule is seen as a good parameter to predict its (passive) absorption into the body. It is defined as the surface area of nitrogen and oxygen atoms in a molecule plus the surface of the hydrogens attached to these hetero-atoms.
It has been established that a PSA value of over 140 Å2 generally yields molecules that are poorly absorbed from stomach and gastro-intestinal tract, whereas values below 60-70 Å2 suggest potential penetration of the blood-brain barrier, which, of course, is needed for CNS-active drugs.
CIDRUX has developed a software package for the accurate calculation of PSA values, called SurfArea. The program comes with a template file of drug molecules to allow a quick taste of the program’s capabilities. The 3D structures are nicely displayed and can be easily manipulated. In fact, any atom surface can be calculated instantaneously. The program runs on any PC with a Windows operating system (Windows98 and higher).
Why don’t you download it – it’s easy to use, intuitive, and absolutely free!
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