Fentanyl and Alfentanil Arterial Concentrations (Circles) and Electroencephalographic (EEG) Response (Irregular Line) to an Intravenous Infusion Alfentanil Shows a Less Time Lag Between the Rise and Fall of Arterial Concentration and the Rise and Fall of EEG Response Than Fentanyl Because It Equilibrates With the Brain More Quickly.

(Reused from Scott JC, Stanski DR. Decreased fentanyl and alfentanil dose requirements with age. A simultaneous pharmacokinetic and pharmacodynamic evaluation. J Pharmacol Exp Ther. 1987;240:159-166.)

Fentanyl and alfentanil arterial concentrations (circles) and electroencephalographic (EEG) response (irregular line) to an intravenous infusion. Alfentanil shows a less time lag between the rise and fall of arterial concentration and the rise and fall of EEG response than fentanyl because it equilibrates with the brain more quickly.