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Encyclopedia of Physical Science and Technology EN011J-559 July 25, 2001 18:57

Pharmacokinetics

Michael F. Flessner
University of Rochester

I. Basic Pharmacokinetic Concepts
II. Drug Absorption
III. Drug Distribution
IV. Drug Metabolism and Elimination
V. Pharmacokinetic Variability
VI. Quantitative Approaches to Pharmacokinetic
Modeling

GLOSSARY Volume of distribution Apparent volume to which a
dose of drug distributes at the time of injection or
Active transport Typically drug transport via a spe- administration.
cific transporter, requiring energy, and moving solute
against its electrochemical gradient.
Bioavailability Fraction of drug absorbed unchanged PHARMACOKINETICS is the science of quantitation of
into the target compartment. drug absorption, distribution, and elimination within bio-
Drug clearance Volume of distribution cleared of drug logical organisms. It is a subset of pharmacology, which
per unit time. is the study of drugs, their sources, different preparations,
Half-life Time required for the concentration of a drug to and therapeutic uses. On the other hand, pharmacody-
decrease by one half (t 1/2 ). namics is the study of the specific cellular and molecular
Passive transport mechanisms Mechanisms that use the actions of a drug on a biological organism. Figure 1 il-
forces of concentration differences (diffusion) or pres- lustrates these definitions for the general case. Together,
sure differences (convection) to move substances from pharmacokinetics and pharmacodynamics encompass the
one site to another. entire process of drug entry into the body of the organism
Pharmacodynamics The study of the specific cellular to the ultimate biological effect. This article will focus
and molecular action of a drug on a biological on pharmacokinetics, which applies mathematics to the
organism. following questions:
Pharmacokinetics The science of quantitation of drug
absorption, distribution, and elimination within biolog- 1. How quickly and how much of a drug enters the
ical organisms. It is a subset of pharmacology. organism?
Pharmacology The study of drugs, their sources, differ- 2. To where does the drug distribute?
ent preparations, and therapeutic uses. 3. How rapidly is the drug removed from the body?

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