Single-dose input systems

The differential equation and its solution that describe this model are given by 

Zero-order input and one-compartment disposition (I0D1). This model and the I0D1 model only differ from the first model (IBD1) by the kinetic order of the input the disposition component remains the same. The compartmental box diagram is shown in Fig. 1.11. The differential 

First-order input and one-compartment disposition (11D1). In this model, the input is first order, and the disposition is one compartment. The 

Instantaneous input and two-compartment disposition (IBD2). The IBD2 

The central compartment represents the blood/plasma and any other tissue that rapidly equilibrates, relative to the distribution rate, with the blood/plasma (e.g., liver or heart tissue). The tissue compartment represents all other tissues that keep the drug and reach steady-state concentrations more slowly than the tissues of the central compartment. Since the two-compartment model is fairly robust in describing a bulk of all drugs, we will limit our discussion to two compartments with elimination 

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In the previous discussion of the one- and two-compartment models we have loaded the system with a single-dose D at time zero, and subsequently we observed its transient response until a steady state was reached. It has been shown that an analysis of the response in the central plasma compartment allows to estimate the transfer constants of the system. Once the transfer constants have been established, it is possible to study the behaviour of the model with different types of input functions. The case when the input is delivered at a constant rate during a certain time interval is of special importance. It applies when a drug is delivered by continuous intravenous infusion. We assume that an amount Z) of a drug is delivered during the time of infusion x at a constant rate (Fig. 39.10). The first part of the mass balance differential equation for this one-compartment open system, for times t between 0 and x, is given by ... 

Methods to estimate dose resulting from release of the source term are based on a database of airborne dose versus distance calculations for single isotope releases from TA-V facilities (Naegeli 1999). The database was developed using the Melcor Accident Consequence Code System Version 2 (MACCS2) computer model with a standard input for each single isotope calculation. Combining doses for individual isotopes provides the dose from the released source term. 

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