Slopes, rates and derivatives

A straight line has a slope which is constant. This constant slope, AylAx, is the change in y divided by the change in x. By contrast, in a curved line, there is an instantaneous slope at each point along the curve (calculated by finding the slope of the tangent to that particular point). This instantaneous slope also goes by the name of the derivative dy/dx. We will now demonstrate the concept of slope as it arises in pharmacokinetics. 

The simplest pharmacokinetic model (as we shall see in subsequent chapters, this is an intravenous injection of a one-compartment drug eliminated by a first-order process) is described by a single-term exponential equation  

When is a variable not a variable Answer, when it is a parameter. 

The answers to these questions suggest that a parameter is something between a variable and a constant. This is approximately true but the very specific meaning of parameter in pharmacokinetics is  

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