Lecture Notes: Principles of Drug Action

Overview

• Focus on chapters 4, 5, and 8
• Topics include pharmacokinetics, pharmacodynamics, drug development, and effects on older adults
• Importance of understanding drug actions, side effects, and barriers in the body

Pharmacokinetics

• Definition: Study of how drugs move through the body
• Purpose: Predict drug actions and side effects
• Barriers: Membranes like the blood-brain barrier and placental barrier
• Processes: Absorption, distribution, metabolism, excretion

Absorption

• Movement from administration site to bloodstream
• Factors affecting absorption:
  • Formulation (liquids absorb faster than pills)
  • Dose (higher doses absorb differently)
  • Route of Administration:
    • Fastest: IV, then IM, subq, PO, transdermal
  • Drug molecule size
  • Surface area of absorption site
  • Digestive motility
  • Blood flow
  • Food and dietary interactions
  • Degree of ionization and pH

Distribution

• Definition: How drugs are transported to target areas
• Factors:
  • Blood flow to tissues
  • Tissue affinity for drugs (bone, teeth, fat)
  • Drug-protein complexes may hinder distribution
  • Competition for binding sites can increase toxicity risk

Metabolism

• Primary Site: Liver
• Processes:
  • Hepatic enzymes inactivate drugs for excretion
  • Enzyme induction increases liver activity
  • Enzyme inhibitors decrease liver activity
• Genetic Variations: Affects drug metabolism
• First-Pass Effect: Liver inactivates some drugs before they reach systemic circulation

Excretion

• Primary Site: Kidneys
• Excreted Substances: Free drugs, water-soluble agents, electrolytes
• Factors:
  • Kidney function (renal failure affects excretion)
  • Other excretion methods: respiratory, sweat, bile

Drug Concentration & Effects

• Concentrations:
  • Minimum effective concentration
  • Toxic concentrations
  • Therapeutic range
  • Therapeutic index: Narrow or wide window
• Pharmacokinetic Terms:
  • Onset, peak, duration, half-life, trough

Pharmacodynamics

• Definition: How drugs affect the body
• Processes: Clinical trials to determine effects
• Dose-Response Curves:
  • Median effective dose
  • Median lethal dose
  • Median toxicity dose
• Drug Safety: Therapeutic index reflects safety margins

Drug Interactions

• Types:
  • Addition (combo drugs)
  • Synergism (greater combined effect)
  • Antagonism (blocking effects)
  • Displacement (replacing effects)

Older Adults

• Considerations:
  • Decreased gastric motility, reduced liver and kidney function
  • Increased body fat, decreased muscle mass
  • Risk of drug accumulation and toxicity
• Monitoring: Liver and kidney function tests are crucial

Conclusion

• Complex interactions in drug absorption, distribution, metabolism, and excretion must be understood to ensure effective and safe drug administration.
• Special considerations for different populations, such as older adults, need to be taken into account.

• Questions should be directed to the discussion board.