The receptor-site theory.
c. Antagonists. Antagonists are drugs that will or reverse block the action of
other drugs. There are two types of antagonists: competitive and physiological.
(1) Competitive antagonists. Competitive antagonists combine with the
receptor-site and prevent another drug from combining with the receptor-site. A
competitive antagonist does not displace a drug at the receptor-site. Figure 3-6
illustrates the concept of a competitive antagonist.
Figure 3-6. A competitive antagonist.
(2) Physiological antagonists. Physiological antagonists reverse the action
of the drug by acting on a different receptor-site to cause a different physiological effect.
3-15. DRUG EFFICACY
a. Drug efficacy refers to the effectiveness of a drug. Drug efficacy is measured
by the clinical response of the patient. A drug is considered to have a high degree of
efficacy, if it achieves desired clinical results.
b. Laboratory tests may be used to determine the amount of drug that has been
absorbed. The amount of drug absorbed may be used to predict a patient's response.
However, since people respond differently to the same dose of the same drug, merely