Dose-Response Relationship

Dose-Response Relationship describes how the magnitude of a drug’s effect changes with different doses, showing potency and efficacy.

• The dose-response relationship explains how a drug’s effect changes with varying doses—central to pharmacodynamics.

1. Graded Dose-Response

   • Measures the intensity of response in an individual as dose increases.
   • Displayed as a sigmoidal (S-shaped) curve on a semi-log graph.

   • Phases of the Curve:

     • Threshold – Minimum dose with a measurable effect.
     • Linear (log) phase – Effect increases proportionally with dose.
     • Plateau – Maximum effect (Emax); further dosing has no added effect.

   • Key Terms:

     • Emax: Maximum achievable effect.
     • EC50: Dose producing 50
     • Potency: Lower dose needed for effect = more potent.
     • Efficacy: Maximum effect a drug can achieve.
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2. Quantal Dose-Response

   • Measures all-or-none effects (e.g., sleep, death) across a population.
   • Curve shows

   • Key Terms:

     • ED50: Dose causing desired effect in 50
     • TD50: Dose causing toxicity in 50
     • LD50: Dose causing death in 50
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   • Therapeutic Index (TI):

     • TI = TD50 / ED50
     • Indicates drug safety—higher TI = safer drug.

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