WEEK 2

• Pharmacodynamics is the study of the effect of drugs on the body
• Drugs act within the body to mimic the actions of the body’s own chemical messengers
• Pharmacodynamics involves the interactions between the chemical components of living systems and foreign chemicals, including drugs, that enter those systems
• Drugs work in one of four ways:

  • To replace or act as a substitute for missing chemicals
  • To increase or stimulate certain cellular activities
  • To depress or slow cellular activities
  • To interfere with the functioning of foreign cells invading
• Dose-response relationship is the body’s physiological response to changes in drug concentration at the site of action
• Potency refers to the amount of drug needed to elicit a specific physiologic response to a drug
• Efficacy is the magnitude of effect a drug can cause when exerting its maximal effect
• Maximal efficacy is the point at which increasing a drug dosage no longer increases the desired therapeutic response
• Therapeutic index (TI) describes the relationship between the therapeutic dose of a drug (ED50) and the toxic dose of a drug (TD50)
• Therapeutic dose of a drug (ED50) is the dose of a drug that produces a therapeutic response in 50% of the population
• Toxic dose of a drug (TD50) is the dose that produces a toxic response in 50% of the population
• Onset is the time it takes for a drug to reach the minimum effective concentration (MEC) after administration
• Peak occurs when the drug reaches its highest concentration in the blood/plasma concentration
• Duration of action is the length of time the drug exerts a therapeutic effect
• Therapeutic drug monitoring involves determining drug concentration by measuring peak and trough drug levels
• Theories of drug action:

  • Drug-receptor interaction
  • Drug-enzyme interaction
  • Nonspecific drug interaction
  • Selective toxicity
• Drug response can be primary (always desirable/physiologic effects) or secondary (desirable or undesirable effects)
• Classification of drug action:

  • Rapid (few seconds to minutes)
  • Intermediate (1-2 hours after administration)
  • Delayed/Slow (several hours after administration)
• Categories of drug action:

  • Stimulation/Depression
  • Replacement
  • Inhibition/Killing of organism
  • Irritation
• Drug-drug interactions:

  • Additive effect
  • Synergistic effect
  • Potentiation
  • Antagonistic effect
• Adverse drug effects:

  • Side effects
  • Allergic reactions
  • Idiosyncratic reactions
  • Toxicity
  • Iatrogenic responses