Fig. 1. The kinetic models for intravenous (IV) and inhalation (INH) administration of morphine. The intravenous model contains a lag time, indicated by δ, to account for the delay from administration to first appearance of the drug at the sample site. The inhalation model contains a two-compartment absorption model to describe the uptake of aerosolized drug, in which these two compartments are indicated by A and B. In both models, the drug is then deposited into the central compartment (1) of a standard three-compartment systemic model containing two peripheral compartments (2 and 3).