Data vs Models of System

Suppose one has a set of pharmacokinetic data. The question is how to obtain information from the data related to the disposition of the drug in question. DiStefano and Landaw (22) deal with this question by making the distinction between models of data and models of system. Understanding this distinction is useful in understanding the differences between compartmental and noncompartmental models. 

As discussed, the noncompartmental model divides the system into two components an accessible pool and nonaccessible pools. The kinetics of the nonacces-sible pools are lumped into the recirculation-exchange arrows. From this, as has been discussed, we can estimate pharmacokinetic parameters describing the accessible pool and system. 

What happens in the compartmental model framework Here the most common way to deal with pharmacokinetic data is to fit them first by a sum of exponentials, since, in a linear, constant-coefficient system, the number of exponential phases in the plasma level-vs-time curve equals the number of compartments in the model. 

Consider the situation in which plasma data are obtained following a bolus injection of the drug. Then the data can be described by 

FIGURE 8.7 Twro two-compartment models in wliich drug is administered intravenously into compartment 1 samples are taken from this compartment. See text for explanation. 

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Pharmacokinetic Anaiysis Models of Data vs Models of System... 

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