The strength of a drug action is determined by the dose administered to a
patient and how frequently the dose is administered. The first dose is called
a loading dose or priming dose and consists of a large concentration of the drug.
Subsequent doses are called maintenance doses and consist of a normal concen-
tration of the drug.
Drug activity is divided into the pharmaceutic phase, pharmacokinetic phase;
and the pharmacodynamic phase. The pharmaceutic phase is the disintegration
and dissolution of a drug taken orally. The pharmacokinetic phase is the mecha-
nism used to absorb, distribute, and eliminate a drug. The pharmacodynamics is
a drug’s effect on the physiology of the cell and the mechanism that causes the
pharmaceutical response.
Drugs bind to receptors on the cell membrane called reactive cellular sites.
Receptors are proteins, glycoproteins, proteolipids, or enzymes. Depending on
the drug, binding either initiates a physiological response by the cell or blocks a
cell’s physiological response. A drug that causes a physiological response is called
an agonist. A drug that blocks a physiological response is called an antagonist.
The safety of a drug is identified by the drug’s therapeutic index. A low ther-
apeutic index means a drug has a narrow margin of safety requiring that that the
drug’s peak level and trough levels be closely monitored. A high therapeutic
index means a drug has a broad margin of safety and does not require frequent
monitoring of the patient and the serum drug level.
Now that you have a good understanding of the theory of how drugs work, in
the next chapter we’ll turn our attention to the practical aspect of pharmacology
and see how pharmacology is used in the nursing process.
Quiz
- The pharmacokinetic phase is
(a) the form of the drug.
(b) the way the drug is absorbed, distributed, and eliminated.
(c) the effect the drug has on the body.
(d) none of the above. - The ingredient in a drug that causes a physiological response is called
(a) D-fill.
(b) excipient.
(c) D-active.
(d) particle.
CHAPTER 2 Drug Action and Drug Interactions^39