Lecture Notes: Introduction to Pharmacodynamics

Overview

• Pharmacokinetics: Study of how the body affects a drug through absorption, distribution, metabolism, and excretion.
• Pharmacodynamics: Study of how drugs affect the body, examining the mechanisms that produce a cellular response.

Key Concepts

Drug-Receptor Interaction

• Proteins as Targets: Most drugs interact with receptor proteins found in the cell membrane, cytoplasm, or nucleus.
• Receptors and Ligands: Receptors have ligands (molecules) that fit into their active sites, causing conformational changes and signal propagation.

Types of Drug Actions

• Agonists: Drugs that mimic native ligands, activating receptors and facilitating typical responses.
• Antagonists: Drugs that bind to receptors but do not activate them, keeping them in an inactive state (inhibitors/blockers).

Binding Equilibrium

• Ligand (L) and Receptor (R) Interaction: Represented as L + R ↔ LR, where LR is the ligand-receptor complex.

Potency vs. Efficacy

• Potency:
  • Refers to the concentration or dosage required to produce 50% of the drug's maximal effect.
  • Assessed through dose-response curves.
  • Correlates with the x-axis (dosage) on the curve.
• Efficacy:
  • Maximum effect a drug can achieve, beyond which no further effect is observed with increased dosage.
  • Correlates with the y-axis (effect) on the curve.

Factors Affecting Efficacy

• Binding Affinity:
  • How well a drug binds to its target's active site, influenced by electrostatic interactions, hydrogen bonds, and potentially covalent bonds.
  • Higher binding affinity means higher efficacy, especially for inhibitors.
• Agonists and Inhibitors:
  • Agonists require the right functional groups for conformational changes akin to native ligands.
  • Inhibitors need high binding affinity to prevent displacement by native ligands.

Conceptualizing Potency and Efficacy

• Potency is related to the affinity for a receptor.
• Efficacy is related to the clinical effect once the drug is bound.

Conclusion

• Understanding pharmacokinetics and pharmacodynamics is crucial before studying specific drugs’ mechanisms of action.
• Future lectures will dive into specific drug examples, reinforcing these concepts.

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