Physicochemical Properties of the Drug
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Just as the absorption and distribution of a drug are influenced by its physicochemical properties, so is its interaction with the drug metabolising enzymes.
PHYSICOCHEMICAL PROPERTIES OF THE DRUG
Just as the absorption and distribution of a drug
are influenced by its physicochemical properties, so is its interaction with
the drug metabolising enzymes. Molecular size and shape, pKa,
acidity/basicity, lipophilicity and steric and electronic characteristics of a
drug influence its interaction with the active sites of enzymes and the
biotransformation processes to which it is subjected. However, such an
interrelationship is not clearly understood.
Stereochemical nature of drug also influences its
metabolism. Biotransformation requires interaction of a drug with an enzyme,
which is an interaction where spatial arrangement is critical. Many drugs that
undergo metabolism exhibit stereoselective hepatic clearance, for example, the
oral clearance of verapamil, a drug with high intrinsic clearance, displays
profound stereoselectivity such that clearance ratio of +/- isomers is
approximately 4.
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