Introduction to Nursing Pharmacology Nursing Pharmacology

Drugs and The Body

Drugs and the Body


  • Pharmacodynamics is the science of dealing with interactions between living organisms and foreign chemicals
  • Chemical reactions occur continuously in the body of each living system
  • When other chemicals (drugs) are added to the body, additional effects occur

Drug Actions

  • To replace or act as substitutes for missing chemicals
  • To increase or stimulate certain cellular activities
  • To depress or slow certain cellular activities
  • To interfere with the functioning of foreign cells

Receptor Cells

  • Receptor site reacts to certain chemicals
  • The better the fit between receptor site and chemical, the more pronounced the reaction
  • Enzymes within the body are needed to break down the chemicals to open up the receptor site

Lock & Key

Drugs and The Body: Lock and Key
Drugs and The Body: Lock and Key


  • Drugs can interfere with the enzymes that may be catalysts for chemical reactions
  • Enzymes produce a cascade effect


  • Onset of drug action
  • Drug half-life
  • Timing of the peak effect
  • Duration of drug effects
  • Metabolism or biotransformation of the drug
  • Site of excretion

The Processes by Which Drugs Are Handled in the Body

The Processes by Which Drugs Are Handled in the Body
The Processes by Which Drugs Are Handled in the Body


  • Critical concentration
    • The amount of a drug that is needed to cause a therapeutic effect
  • Loading dose
    • A higher dose than that usually used for treatment
  • Dynamic equilibrium
    • The actual concentration that a drug reaches in the body

Dynamic Equilibrium

  • The actual amount of drug that reaches the body results in a dynamic equilibrium
  • Dynamic equilibrium is affected by:
    • Absorption
    • Distribution
    • Biotransformation
    • Excretion


  • Administration
    • Affected by route of administration
    • Oral medications affected by presence of food in the stomach
  • First-pass effect
    • Medications are extensively metabolized by the liver

Factors Affecting Absorption

Factors That Affect Absorption of Drugs
Factors That Affect Absorption of Drugs


  • Protein binding
  • Blood–brain barrier
  • Placenta/breast milk


  • The liver is the single most important site for biotransformation (metabolism)
  • This process breaks down medications
  • It helps to prevent medications from causing adverse effects on the body


  • Removal of drugs from the body
  • Kidneys play the most important role in the excretion of medication


  • Half-life is the time it takes for the amount of drug in the body to decrease to one-half the peak level
  • Half-life is affected by the absorption, distribution, metabolism, and excretion





Calculating Half-Life

Focus on Calculations
Focus on Calculations

Factors Influencing Drug Effects

  • Weight
  • Age
  • Gender
  • Physiologic factors
  • Pathologic factors
  • Genetic factors
  • Immunologic factors
  • Psychological factors
  • Environmental factors
  • Drug tolerance
  • Cumulative effect

Drug-to-Drug Interactions

  • Can occur any time two or more drugs are taken together
  • Can occur at:
    • Site of absorption
    • During distribution
    • During biotransformation
    • During excretion
    • At the site of action

Drug–Food Interaction

  • Certain foods interact with drugs
  • Drugs are best taken on an empty stomach

Drug–Laboratory Test Interaction

  • Drugs may alter the results of lab testing
  • Laboratory tests may be used to monitor the effects of other medications