For all the induction agents, the initial rapid decline in plasma concentration seen after a single IV bolus dose is due largely to the distribution to other tissues.

The rate at which induction agents are metabolized varies according to the agent.

Etomidate is an ester and is rapidly broken down by plasma and hepatic esterases.

Propofol and thiopental are metabolized by the liver. Propofol is much more rapidly broken down than thiopental and has no active metabolites, whereas thiopental is metabolized more slowly, but has an active metabolite-pentobarbital.

After a single IV bolus dose of thiopental for induction, the concentration of pentobarbital is very low and does not influence the duration of action of thiopental; it becomes more important if thiopental is given by a continuous infusion.