Drug action pharmacodynamic phase

Define the terms pharmacokinetic phase and pharmacodynamic phase in the context of drug action. List the main general factors that affect these phases. 

Shape and stereochemical. These properties affect the pharmacodynamic phase of drug action and influence the drug s interaction with its target receptor. Shape and stereochemical properties describe the structural arrangement of the drug molecule s constituent atoms and influence the molecule s final approach toward the target receptor. 

Electronic. Electronic properties also affect the pharmacodynamic phase of drug action. The electronic properties of a molecule are governed by the... 

In the foregoing sections, pharmacon metabolism has been considered in relation to the pharmacodynamic, especially toxic aspects of action. Drug distribution also plays a role in the pharmacodynamic phase of drug action. Modulation of drug distribution, for instance, exclusion of penetration of particular barriers in the organism (e.g. the blood-brain barrier), or preferential bioactivation or bioinactivation in particular tissues, can modulate the spectrum of action of compounds and possibly exclude particular undesired effects. 

The pharmacodynamics phase corresponds to the way in which a drug binds to receptors, transporters, and channels in order to elicit a particular action from a cell (this is called signal transduction). This is referred to as the mechanism of action. While researchers attempt to determine the mechanism of action of promising compounds in order to better predict therapeutic outcomes and unexpected effects, often times the exact mechanism remains unknown, even after the drug has been approved for use. 

FIGURE 1 Pharmacokinetics versus pharmacodynamics. Pharmacokinetics deals with the phases of drug absorption, drug distribution, and drug elimination. Pharmacodynamics defines the biological effect of a drug at a site of action. 

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