4.2 - Essentials of Drug Action

• where and how the effect is produced (MOA)

  drug action
• what is produced by the drug, consequence of

  the drug-receptor interaction

  drug effects
• Aspirin blocks the synthesis of prostaglandins which mediates the raising of the body thermostat by the hypothalamus (DA), reducing fever (DE)
• Categories of Drug Action

  • Stimulation or Depression:
  • Replacement
  • Inhibition or killing organisms
  • Irritation
• acts to increase or decrease activity of physiological function

  Stimulation or Depression
• in therapy for deficiencies e.g diabetes mellitus


  Replacement
• antibiotics, antifungals, antiparasitics

  Inhibition or killing organisms
• antiparasitics, anthelminthics

  Irritation
• Categories of Drug Effect

  • Physiologic Effect
  • Pharmacologic Effect
• retains the normal function of

  the biologic system

  Physiologic Effect
• side effects resulting from the lack of specific action while binding to other tissues

  Pharmacologic Effect
• Categories of Drug Effect

  • Drug Toxicity
  • Allergic Reactions
  • Idiosyncratic Reactions
• predictable adverse effect of the drug related to the dose administered (range between therapeutic and toxic dose is known as drug safety)

  Drug Toxicity
• unpredictable adverse effects due to the response of the patient’s immune system

  Allergic Reactions
• due to genetic differences of patient occurring at the 1st exposure of the drug

  Idiosyncratic Reactions
• Drug Effects Enhancement

  • Additive Effects
  • Synergism
  • Potentiation
• if two drugs with the same effect produces an effect equal in magnitude to the sum of individual effects (1+1=2)

  Additive Effects
• if two drugs with the same effect produces an effect greater in magnitude than sum of individual effects (1+1=3)

  Synergism
• occurs if a drug lacking an effect of its own increases the effects of a second active drug (0+1=3)

  Potentiation
• Parameter that characterizes drug activity

  • describes the nature of drug action, potency of the drug, and presence of competitive or non- competitive antagonism
• 2 Types of Dose Response Relationship

  1. Graded dose response
  2. Quantal dose-response relationship
• • refers to the rate of change in the intensity of response proportional to the rate of change of drug concentration
  • higher dose, greater response


  Graded dose-response relationship
• Graded dose-response relationship characteristic variables

  • Potency
  • Slope of the curve • Variability in response • Maximal effect
• refers to the dose needed to produce an effect (smaller dose, greater potency)

  Potency
• indicates the range of dosage to which the drug acts

  Slope of the curve
• depends on physiological, pathological, or drug induced problem in the patient


  Variability in response
• peak response possible for the effector

  Maximal effect
• • all-or-none response
  • measures the frequency in which a dose of a drug produces a pharmacological effect in a population

  Quantal dose-response relationship
• Quantaldose-response relationship

  • assumes that an individual responds to their maximum capability or none at all
  • the graph assumes a Gaussian or normal distribution curve
• used in clinical trials before a drug is marketed for use

  Quantal dose-response relationship