Learning Objective

Understand the concept of quantal (cumulative) dose-response curves, their use in estimating population-based drug effects (e.g., ED50), and how curve shape reflects intersubject variability.

Quantal (Cumulative) Dose-Response Curves

A quantal dose-response (D-R) curve plots the percentage of a population showing a specified effect versus the dose or log dose of a drug. Unlike graded D-R curves, which measure the magnitude of effect in a single individual or system, quantal curves focus on all-or-none responses across a population.

Median Effective Dose (ED50):

• Dose at which 50% of the population exhibits the defined effect.

Variability in response:

• Steep curve: Most subjects respond at similar doses → low intersubject variability.
• Flat curve: Wide range of doses needed for effect → high intersubject variability.

Applications:

• Estimating safe and effective dosing in populations.
• Comparing potency and variability between drugs.

Activity