Pharmacodynamics Overview Quiz

Study Notes

Describes how drugs produce effects in the body.
Includes four main mechanisms:
- Drug-receptor interaction: Drugs bind to specific molecules (receptors) to trigger an effect.
- Ion channel modulation: Drugs can influence the opening or closing of channels that allow ions to pass through cell membranes.
- Enzyme activity: Drugs can either inhibit or activate enzymes involved in various biochemical processes.
- Carrier molecule interaction: Drugs can interfere with or facilitate the transport of substances across cell membranes.

Drug receptors are usually proteins that bind drugs and mediate their effects.
Binding of a drug to its receptor forms a drug-receptor complex (DR) which initiates the biological response.

Affinity: Measures how tightly a drug binds to its receptor.
Efficacy: The drug's ability to induce a therapeutic response once bound to the receptor.
Potency: The drug's strength, measured by the amount needed to produce a specific effect.

Agonist: A drug that activates a receptor, producing a similar effect to the body's natural signaling molecules.
Antagonist: A drug that blocks the action of an agonist at a receptor, without having any effect of its own.

Addition: The combined response of two drugs equals the sum of their individual effects.
Synergism: Two drugs with the same effect produce a greater response than the sum of their individual effects.
Potentiation: A drug with no effect on its own enhances the effect of a second drug.
Antagonism: One drug inhibits the effect of another drug.

The dose of drug required to produce a defined therapeutic response in 50% of the population.
ED50 is often considered a standard starting dose for treatment.

The dose of drug that causes adverse effects in 50% of subjects treated, at an intensity or frequency incompatible with the targeted indication.

Side Effects: Unavoidable, unintended pharmacodynamic effects occurring at a therapeutic dose.
Toxic Effects: Result from excessive drug action due to overdosing or prolonged use.
Drug Intolerance: Side effects of a drug in an individual at therapeutic doses.
Drug Tolerance: Decreased response to a specific dose of drug after repeated administration.

Patients who are tolerant to a drug require higher doses to achieve the same effects that could be achieved with lower doses previously.
There are three types of tolerance:
- Pharmacodynamic tolerance: Occurs when the body adapts to the drug's effect at the receptor level.
- Pharmacokinetic (metabolic) tolerance: Occurs when the body metabolizes the drug more quickly, reducing its effective serum concentration.
- Tachyphylaxis: A rapid decrease in response after repeated drug administration, often within a short period.