Home Books Katzung & Trevor's Pharmacology: Examination & Board Review, 10e

Chapter 2. Pharmacodynamics

Pharmacodynamics deals with the effects of drugs on biologic systems, whereas pharmacokinetics (Chapter 3) deals with actions of the biologic system on the drug. The principles of pharmacodynamics apply to all biologic systems, from isolated receptors in the test tube to patients with specific diseases.

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Receptor

A molecule to which a drug binds to bring about a change in function of the biologic system

Inert binding molecule or site

A molecule to which a drug may bind without changing any function

Receptor site

Specific region of the receptor molecule to which the drug binds

Spare receptor

Receptor that does not bind drug when the drug concentration is sufficient to produce maximal effect; present when Kd > EC50

Effector

Component of a system that accomplishes the biologic effect after the receptor is activated by an agonist; often a channel or enzyme molecule, may be part of the receptor molecule

Agonist

A drug that activates its receptor upon binding

Pharmacologic antagonist

A drug that binds without activating its receptor and thereby prevents activation by an agonist

Competitive antagonist

A pharmacologic antagonist that can be overcome by increasing the concentration of agonist

Irreversible antagonist

A pharmacologic antagonist that cannot be overcome by increasing agonist concentration

Physiologic antagonist

A drug that counters the effects of another by binding to a different receptor and causing opposing effects

Chemical antagonist

A drug that counters the effects of another by binding the agonist drug (not the receptor)

Allosteric agonist, antagonist

A drug that binds to a receptor molecule without interfering with normal agonist binding but alters the response to the normal agonist

Partial agonist

A drug that binds to its receptor but produces a smaller effect at full dosage than a full agonist

Inverse agonist

A drug that binds to the inactive state of receptor molecules and decreases constitutive activity (see text)

Graded dose-response curve

A graph of increasing response to increasing drug concentration or dose

Quantal dose-response curve

A graph of the fraction of a population that shows a specified response at progressively increasing doses

EC50, ED50, TD50, etc

In graded dose-response curves, the concentration or dose that causes 50% of the maximal effect or toxicity. In quantal dose-response curves, the concentration or dose that causes a specified response in 50% of the population under study

The concentration of drug that binds 50% of the receptors in the system

Efficacy, maximal efficacy

The maximal effect that can be achieved with a particular drug, regardless of dose

Receptors are the specific molecules in a biologic system with which drugs interact to produce changes in the function of the system. Receptors must be selective in their ligand-binding characteristics (so as to respond to the proper chemical signal and not to meaningless ones). Receptors must also be modifiable when they bind a drug molecule (so as ...

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