Multicompartment model

This is the closed from solution to the 2-compartment model.

$$X = dose \times \left(A e^{-\alpha t} + B e^{-\beta t} \right)$$

What are A and B, alpha and beta? Horrible combinations of the various ks in the model.

Distribution phase:

Rapid loss of solute from central compartment into peripheral compartment

Elimination phase:

Slow elimination of solute from central compartment

Falling central concentration drives redistribution from peripheral compartment

"Time taken for a drug to fall to half it's initial plasma level after stopping an infusion."

Depends on:

1. Duration of infusion (longer \(\to\) more accumulation in peripheral compartments)
2. VdSS (higher \(\to\) less drug in unbound plasma to be cleared)
3. Elimination rate constant

Volume of distribution at steady state. Equal to the sum of all the volumes of all the compartments!