The reaction of the body to a dose of medicine can sometimes...

The reaction of the body to a dose of medicine can sometimes be represented by an equation of the form $$R=M^{2}\left(\frac{C}{2}-\frac{M}{3}\right)$$ where $C$ is a positive constant and $M$ is the amount of medicine absorbed in the blood. If the reaction is a change in blood pressure, $R$ is measured in millimeters of mercury. If the reaction is a change in temperature, $R$ is measured in degrees, and so on. Find $d R / d M .$ This derivative, as a function of $M,$ is called the sensitivity of the body to the medicine. In Section $4.5,$ we will see how to find the amount of medicine to which the body is most sensitive.

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Key Concepts

Derivative as a Rate of Change

The derivative of a function quantifies how the function value changes as its input changes. In the context of medicine and physiology, the derivative represents the sensitivity, which indicates how the body’s reaction (such as changes in blood pressure or temperature) responds to changes in the dosage of medicine.

Product Rule

The product rule is a fundamental technique in differentiation used when the function to be differentiated is the product of two functions. In this problem, the reaction R is expressed as the product of M² and another function of M, necessitating the use of the product rule to differentiate correctly.

Power Rule

The power rule is a basic rule in calculus that simplifies the differentiation of functions in the form of a constant times a variable raised to an exponent. This rule is particularly useful when differentiating polynomial terms like M² and M/3, as seen in the reaction equation.

Sensitivity in Pharmacodynamics

In the study of pharmacodynamics, sensitivity refers to how responsive a biological system is to changes in medication dosage. The derivative dR/dM computed in this problem is a mathematical representation of this sensitivity, showing the rate at which the body’s reaction changes with respect to the medicine absorbed.

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