Pharmacodynamics Overview

Pharmacodynamics Overview

• Pharmacodynamics is the study of how a drug affects the body
• It focuses on the mechanisms of action of drugs and the effects they produce.
• It essentially answers the question, "What does the drug do to the body?"

Learning Outcomes

• Define pharmacodynamics
• Explain types of drug receptors, including:
  • Receptors for hormones and neurotransmitters
  • Enzymes
  • Membrane transport molecules
  • Other macromolecules
• Explain drug-receptor interactions
• Define terms related to drug-receptor interactions such as:
  • Agonists
  • Antagonists

Pharmacodynamics vs Pharmacokinetics

• Pharmacodynamics describes what the drug does to the body
• Pharmacokinetics describes what the body does to the drug

Examples

• Drugs can have various effects on the human body

Mechanisms of Drug Action

• Drugs act through diverse chemical mechanisms
• The most common mechanism is drug-receptor interaction.
  • Other mechanisms include interacting with nucleic acids, transport proteins, enzymes, and interfering with osmotic cell balance.

Drug-Receptor Interaction

• To induce therapeutic or harmful effects, drugs bind to receptors in the body. This is the pharmacodynamic phase of drug action.
• Drug-receptor interaction is often described using the "lock-and-key" analogy

Receptors (Locks)

• Tissues use receptors to differentiate between different chemical messengers (e.g., drugs, hormones, neurotransmitters)
• Receptors are protein molecules found within cells or on cell membranes (cell wall)
• Receptors are specific, binding to particular hormones or neurotransmitters

Drug Receptors

• Receptors bind to "chemical messengers" (drugs)
• Drugs' effects stem from their interaction with receptors

Drug Receptors (continued)

• Most receptors bind to one or more endogenous substances (e.g., neurotransmitters).
• The proper binding triggers a signal to the cell, resulting in a response by the cell.

Drug Receptors (continued)

• Binding to receptors or other targets can initiate a signal transduction pathway.
• This cascade of events ultimately produces a physiological effect in the cell.
• Examples include changes to a cell's function, secondary messenger molecules, structural and/or chemical alterations.

Types of Receptors

• Receptors for hormones and neurotransmitters
• Enzymes
• Membrane transport molecules
• Other macromolecules

Hormones and Neurotransmitters

• Hormones are chemical substances produced and secreted by glands, influencing various bodily processes (e.g. growth, mood)
• Neurotransmitters are chemical substances that transmit impulses between nerve cells (neurons)

Hormones and Neurotransmitters (continued)

• Neurotransmitters are released from presynaptic neurons, cross a synapse, and stimulate a postsynaptic neuron.

Receptors for Hormones and Neurotransmitters

• Ligands (drugs, hormones, neurotransmitters) bind to protein molecules within/on cell walls.
• Receptors are classified according to the ligand they bind
• The ligand-receptor binding may be weak and reversible or strong.

Receptors for Hormones and Neurotransmitters (continued)

• Ligand binding to an exterior protein protrusion can modify the receptor and signal the cell.
• The binding can create openings in the cell membrane allowing the passage of specific substances.
• Ligands can pass through cell membranes and connect to receptors within the cell.

Enzymes

• Enzymes are proteins that catalyze intra- or extracellular reactions
• Some membrane-bound enzymes act as receptors, with binding directly affecting the cell.

Membrane Transport Molecules

• Membrane transport proteins facilitate movement across cell membranes.
• Some membrane proteins (channels) allow charged particles to pass through when stimulated.

Membrane Transport Molecules (continued)

• Neurotransmitter transporters prevent neurotransmitters from leaking from the synapse and return them to the presynaptic neuron.

Other Macromolecules

• Steroid receptors move through the cell to the nucleus
• DNA can act as a receptor for substances bound directly to amino acids.
• Lipids and phospholipids, parts of cell membranes, can act as receptors for various substances.

Drug-Receptor Interactions: Binding

• Drugs initiate cellular responses by binding to receptors.
• The drug forms a weak bond with the receptor protein.
• The bond is reversible, so as the drug concentration in the tissue drops, the drug dissociates from the receptor.

Receptor Selectivity

• Receptors are specific molecules, usually proteins, that interact with specific drugs, causing regulatory function changes.

Drug & Specificity

• A drug is any substance that interacts with a molecule or protein in living systems to perform regulatory functions.

Drug-Receptor Interactions: Affinity, Efficacy, and Potency

• Affinity is a drug's ability to link to a receptor.
• Efficacy is a drug's capacity to create the intended cellular effect
• Potency is primarily determined by the drug's receptor affinity.

Drug-Receptor Interaction: Affinity

• Affinity is the tendency of a drug to bind to its receptor.
• The degree of affinity influences the needed concentration of the drug.
• Affinity is a major factor determining drug potency.

Drug-Receptor Interaction: Efficacy

• Efficacy is the ability of a drug to initiate a cellular effect.
• It is independent of affinity, differing among drugs binding to receptors.
• Drugs with both affinity and efficacy are agonists.
• Drugs with affinity but low efficacy are antagonists.

Agonist

• An agonist is a drug binding to and activating a receptor.
• Agonists exhibit both affinity and efficacy for the receptor.
• Agonists result in the binding to the receptor and a physiological response.

Drug Tolerance

• Repeated doses of the same agonist can reduce the responsiveness of receptors.

Antagonist

• An antagonist is a drug that binds to a receptor, preventing its activation.
• Antagonists only have affinity to a receptor, but not efficacy.
• Antagonists block receptor activation by agonists.

Agonists and Antagonists

• Antagonists block receptor activation by agonists
• Agonists activate receptors
• Antagonists bind to receptors, blocking activation,

Class Activity

• Research HMCAS CPGs to list agonists and antagonists

Assignment #2

• Complete an assignment related to pharmacodynamics.

Summary Overview

• Types of receptors
  • Receptors for hormones and neurotransmitters
  • Enzymes
  • Membrane transport molecules
  • Other macromolecules
• Drug-receptor interactions.
  • Agonists/Antagonists

Questions?

• Ask any questions to clarify your understanding of the subject matter.

Explore the fundamentals of pharmacodynamics, the study of drug effects on the body. This quiz covers key concepts such as drug-receptor interactions, types of drug receptors, and fundamental terms like agonists and antagonists. Enhance your understanding of how drugs impact physiological processes.