pharmacology

Pharmacodynamics
DOSE–RESPONSE RELATIONSHIPS
Agonist drugs mimic the action of the original endogenous ligand for the
receptor (for example, isoproterenol mimics norepinephrine on ?1 receptors
of the heart). The magnitude of the drug effect depends on the drug
concentration at the receptor site, which, in turn, is determined by both
the dose of drug administered and by the drug’s pharmacokinetic profile,
such as rate of absorption, distribution, metabolism, and elimination
Graded dose–response relations
As the concentration of a drug increases, its pharmacologic effect also
gradually increases until all the receptors are occupied (the maximum
effect). Plotting the magnitude of response against increasing doses of
a drug produces a graded dose–response curve that has the general
shape . The curve can be described as a rectangular
hyperbola, which is a familiar curve in biology because it can
be applied to diverse biological events, such as enzymatic activity, and
responses to pharmacologic agents. Two important properties of drugs,
potency and efficacy, can be determined by graded dose–response
curves
Potency: Potency is a measure of the amount of drug necessary
to produce an effect of a given magnitude. The concentration
of drug producing 50% of the maximum effect (EC50) is
usually used to determine potency. In Figure 2.7, the EC50 for
Drugs A and B indicate that Drug A is more potent than Drug B,
because a lesser amount of Drug A is needed when compared
to Drug B to obtain 50-percent effect. Therapeutic preparations