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Chapter 3

Principles of Pharmacology



Understanding the use of drugs in the treatment of disease

What the drug does to the body

What the body does to the drug



  • Generic name-Most common name
  • Trade name; brand name (followed by a ® symbol)-Usually easier to pronounce
  • Chemical name-harder to remember, longer names

It is crucial to know the different names of a drug

Drug Names

Antagonist: Drug attaches at drug receptor site, but no chemical drug response is produced and the drug prevents activation of the receptor.

Agonist: Drug attaches at receptor site and activates the receptor; the drug has an action similar to the body's own chemicals. Partial Agonist: Drug attaches at drug receptor site, but only a slight chemical action is produced.

Drug attachment & REceptor sites

Types of Drug Actions

GI tract—passes the fibrous/insoluble waste Kidneys—filters & excretes chemicals that may be made water-soluble Lungs—chemicals may be exhaled Skin—chemicals may be lost through evaporation during sweating

Inactive chemicals, by-products, and waste removal



Biotransformation-Usually occurs in the liver; enzymes break down the chemicals into useful partsFirst-pass effect-Much of the drug is inactivated on it's first pass through the liver before being distributed to the bodyAffected by genetic and developmental factors

Blood system Lymph system Barriers: Blood–brain Placental


Once the drug is absorbed & distributed in the body, it is transformed or altered into active/inactive chemicals



The ways a drug moves by means of circulating body fluids to their sites of action in the body



Absorption processes: Solubility—ability of a drug to dissolve Diffusion—high to lower concentration Filtration—a filter prevents passage of certain molecules Osmosis—diffusion through a semipermeable membrane from a less dense solution to a more dense solution The route of administration influences absorption. EnteralParenteralPercutaneousIntramuscular Percutaneous Sublingual Buccal

How a drug enters the body and passes into the circulation


Basic Drug Processes

Helps explain the dose, frequency, and duration for different drugs.

The amount of time it takes the body to remove 50% of a drug from the body.


Basics of Drug Action

Some common allergies, may be life-threatening; Sulfa, aspirin, penicillin

Anaphylactic reaction

Strange, peculiar, or unpredicted responses;from missing/defective metabolic enzymes, caused by genetic/hormonal


May require hospitalization or be life-threatening

More severe symptoms or problems

These are expected effects; usually GI related

Usually mild, but annoying responses to the drug

When the drug does what is desired & the Therapeutic goal is reached

Expected response of the drug



Hypersensitivity or allergy

Idiosyncratic reactions


Adverse reactions


Side effects


Desired action

  1. Brand name versus generic-Patent for 17 years; brand usually more expensive
  2. Generic equivalent-Identical with respect to active ingredients
  3. Bioequivalent-Chemically the same as the brand name product


One drug making another less effective. Many antibiotics make birth control less effective

Adverse effect

Effects of two drugs taken together where the sum is greater than when taken alone

Synergistic effect

One drug interfering with the action of another. Flumazenil displaces sedative effects of diazepam.

Antagonistic effect

Drugs given together because they have an additive effect and work as a team

Additive effect

When one drug changes the action of another drug. Usually takes place during metabolism.


Drug Interactions

  • Hydration problems
  • Low blood pressure
  • Shock
  • Heart failure
  • Reduced blood flow
  • Ethnicity/Race
  • Body size and lean-to-fat ratio
  • Liver problems

Many drugs can cause interactions with other drugs, so it is vital for nurses to understand possible interactions.

Because both drugs and alochol are processed in the liver, it can cause potential interactions. Alcohol can affect the availability of the drug.

Caffeine can affect the action of some drugs. Some may increase effects of anticlotting drugs. Some can't be taken with aged cheese, red wine, or many processed foods. Certain juices can affect absorption.

Personal Factors

Drugs and laboratory tests

Alcohol interactions

Food interactions

Food, Alcohol, and Drug Interactions

  1. trade and generic name of the drug
  2. the dosage range
  3. the desired action
  4. expected side effects
  5. adverse effects
  6. how to give the drug
  7. important information that you will need to know before to giving the drug

Drug cards should include the following info:

Drug Cards