Generalized multicompartment models

Each of the exponential decay terms in the generalized multicompartment models represent a distinct phase or change in shape of the plasma concentration versus time curve. The extra (n+l) exponential term for first-order absorption always has the absorption rate constant (ka) in the exponent, and always represents an absorption phase. The exponential term with the smallest rate constant (A ) always represents the elimination phase, and this rate constant always represents the elimination rate constant and always equals the terminal line slope m= — A J. All other exponential terms represent distinct distribution phases caused by the different rates of distribution to different tissue compartments. 

Generalized Multicompartment Model until Instantaneous or First-Order Absorption... 

Generalized multicompartment models provide a means of representing highly complex PK situations with relatively simple plasma concentration equations. 

What are some advantages and disadvantages associated with the use of generalized multicompartment models ... 

The research published in this book uses the presently most comprehensive multicompartment model, the first which comprises a coupled atmosphere-ocean general circulation model (GCM). GCMs are the state-of-the-art tools used in climate research. The study is on the marine and total environmental distribution and fate of two chemicals, an obsolete pesticide (DDT) and an emerging contaminant (perflu-orinated compound) and contains the first description of a whole historic cycle of an anthropogenic substance, i.e. from the introduction into the environment until its fading beyond phase-out. 

This assumption is essentially the same for all PK models described in this chapter. See Section 10.7.1.3 for the details regarding this assumption. Unlike the standard one- and two-compartment models, where the equations are written for elimination only from the central compartment (compartment 1), elimination can occur from any one or any combination of model compartments for the generalized multicompartment equations. 

It is not unusual for PK research articles to report model parameters for three-, four-, or five-compartment models for some drugs. If the multicompartment model parameters are known for a drug, then the plasma concentration at any time can be predicted by the equations in Table 10.2. Determining the time at which the plasma concentration reaches a particular value is generally a very laborious trial-and-error calculation, since the concentration equation contains multiple exponential decay terms. An exception occurs for plasma concentration Cf) values at long enough times to be located on the terminal line. For this special case, the time at which a particular plasma concentration is reached is given by... 

Estimation of multicompartment model parameters from measured plasma samples is typically performed utilizing specialized PK software. The general methods are very similar to that used for the previous models. 

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