Questions and Answers
What is pharmacodynamics?
The study of the detailed mechanism of action by which drugs produce their pharmacologic effects.
Which of the following is an example of physical action in non-receptor mediated actions?
What does 'intrinsic activity' or 'efficacy' refer to in pharmacodynamics?
What are ligands in pharmacodynamics?
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Which type of receptor is involved in G protein–coupled receptor (GPCR) signaling?
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Antagonists have intrinsic activity.
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What does the therapeutic index (TI) indicate?
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Which of the following factors does NOT affect drug response?
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What is a full agonist?
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What is 'tolerance' in pharmacodynamics?
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What is 'tachyphylaxis'?
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Study Notes
Pharmacodynamics Overview
- Pharmacodynamics examines how drugs exert their therapeutic effects through interactions with receptors, enzymes, and proteins.
- Mechanisms of action include receptor-mediated and non-receptor-mediated actions.
Mechanisms of Drug Action
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Non-receptor mediated actions:
- Physical Action: Involves physical processes like adsorption (e.g., activated charcoal treating diarrhea).
- Chemical Action: Involves chemical reactions such as neutralizing gastric acid with antacids.
- Enzymatic Action: Drugs can affect enzyme activity (e.g., Neostigmine inhibits acetylcholinesterase).
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Receptor-mediated actions:
- Receptors are macromolecules that selectively bind ligands (drugs) and initiate cellular responses.
- Drug-receptor interactions follow a "lock and key" model based on affinity and intrinsic activity.
Types of Receptors
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Membrane Receptors:
- Ligand-gated ion channels: Open in response to ligand binding; regulate ion flow (e.g., nicotinic acetylcholine receptors).
- G Protein-Coupled Receptors (GPCRs): Activate G proteins to trigger intracellular signaling pathways (e.g., β1 receptors).
- Enzyme-linked receptors: Include protein tyrosine kinases that influence cellular functions (e.g., insulin receptors).
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Intracellular Receptors:
- Located in the cytoplasm; require lipid-soluble ligands that enter the cell (e.g., steroid hormone receptors).
Ligands
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Agonists: Bind to receptors producing a biological response; characterized by both affinity and intrinsic activity.
- Full Agonist: Produces maximal response.
- Partial Agonist: Generates a lesser effect than a full agonist at maximum dosage.
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Antagonists: Bind to receptors but do not activate them, preventing agonist actions.
- Reversible (Competitive): Competes with agonist for binding; can be overcome with increased agonist concentration.
- Irreversible (Non-competitive): Binds covalently, preventing agonist action permanently.
Drug Interactions
- Synergism: Combined effect of drugs is greater than their individual effects.
- Additive Effect: The total effect is the sum of individual actions.
- Antagonism: One drug counteracts the action of another.
Dose-Response Relationships
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Quantal Dose-Response Curve:
- Plots dose against percentage of subjects responding, identifying metrics like ED50 and LD50.
- Therapeutic Index (TI): Indicates drug safety; TI = LD50 / ED50.
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Graded Dose Response Curve:
- Shows the relationship between drug dose and pharmacological response, culminating in maximum efficacy (Emax).
Drug Potency and Efficacy
- Potency: Refers to the dose required to elicit a response (e.g., 1 mg of bumetanide vs. 50 mg of frusemide).
- Efficacy: Reflects a drug's ability to produce a response upon receptor binding.
Factors Influencing Drug Response
- Individual Factors: Body weight, age, sex, species/race, diet/environment, genetic factors.
- Administration Variables: Route of administration and dose impact drug effects.
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Repeated Dosing Effects:
- Cumulation: Accumulation of drugs leading to toxicity (e.g., digoxin).
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Tolerance: Increasing doses required for the same effect due to repeated use.
- Natural Tolerance: Species-level insensitivity (e.g., rabbits and atropine).
- Acquired Tolerance: Develops with continuous exposure (e.g., barbiturate tolerance).
- Tachyphylaxis: Rapid onset of tolerance (e.g., ephedrine after repeated doses).
Conclusion
- Understanding pharmacodynamics is crucial for optimizing drug therapy and managing patient responses effectively.
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Description
This quiz covers the essential concepts of pharmacodynamics, focusing on the mechanisms by which drugs exert their effects. It includes an exploration of drug-receptor interactions and non-receptor mediated actions. Ideal for students studying pharmacology in Spring 2024.
