Which type of response is elicited only when drug concentration exceeds a critical threshold?

Which type of response is elicited only when drug concentration exceeds a critical threshold?

• A. Graded
• B. Quantal
• C. Continuous
• D. Linear

Answer: (B)

In pharmacology, a quantal response is an all-or-none effect in individuals: either the specified response occurs or it does not. Each person has a threshold concentration that must be surpassed for the response to appear. So, the response is elicited only when the drug concentration exceeds that critical threshold, and below it, there is no response. As dose rises, more individuals cross their thresholds, increasing the fraction of responders across the population, which is why the population response is represented as a sigmoid curve. Graded responses, by contrast, vary in magnitude with concentration within an individual and aren’t defined by a strict on/off threshold across a population. Linear or continuous terms aren’t the standard descriptors for this population-level concept. Therefore, the described scenario best fits a quantal response.

In pharmacology, a quantal response is an all-or-none effect in individuals: either the specified response occurs or it does not. Each person has a threshold concentration that must be surpassed for the response to appear. So, the response is elicited only when the drug concentration exceeds that critical threshold, and below it, there is no response. As dose rises, more individuals cross their thresholds, increasing the fraction of responders across the population, which is why the population response is represented as a sigmoid curve.

Graded responses, by contrast, vary in magnitude with concentration within an individual and aren’t defined by a strict on/off threshold across a population. Linear or continuous terms aren’t the standard descriptors for this population-level concept. Therefore, the described scenario best fits a quantal response.