Recovery from a single bolus dose of one of the induction agents is of the order of 5-10 minutes.

The effect of the agent is determined by the brain concentration. The decline in brain concentration lags behind the plasma concentration, but follows a similar time course.

The study of how and why plasma concentrations of drugs change with time is known as 'pharmacokinetics'. Pharmacokinetics is often described as 'what the body does to the drug' to distinguish it from pharmacodynamics, which describes the effects a drug has on the body, i.e. 'what the drug does to the body'.

Fig 1 shows how the plasma concentration of a drug changes with time. There is an initial, very rapid increase in concentration as the administered dose mixes with venous blood and reaches the systemic circulation. In practice, this cannot be measured and is often omitted from the graph. After the peak concentration has been reached, there is an initial rapid rate of decline in concentration that slows as time passes. It takes a long time for all of the drug to disappear from plasma, long after the clinical effect of the drug has worn off.