Pharmacodynamics is the study of the biochemical and physiologic
effects of drugs and their mechanisms of action. It considers
both drug action, which refers to the initial consequence of a
drug-receptor interaction, and drug effect, which refers to the
subsequent effects. The drug action of digoxin, for example, is
inhibition of membrane Na+/K+-ATPase; the drug effect is
augmentation of cardiac contractility. Not all drugs exert their
pharmacologic actions via receptor-mediated mechanisms. The
action of some drugs—including inhalation anesthetic agents,
osmotic diuretics, purgatives, antiseptics, antacids, chelating
agents, and urinary acidifying and alkalinizing agents—is
attributed to their physicochemical properties. Certain cancer
and antiviral chemotherapeutic agents, which are analogs of
pyrimidine and purine bases, elicit their effects when they are
incorporated into nucleic acids and serve as suicide substrates
for DNA or RNA synthesis. The effect of most drugs, however,
results from their interactio