Summary of Pharmacokinetics

Pharmacokinetics involves fundamental physiologic processes, including metabolism, protein binding, tissue distribution, and drug transport into the site of drug effect. Pharmacokinetic models are mathematical relationships between dose and concentration in the plasma or at the site of drug effect. Such models can be used to determine how best to give drugs to achieve a therapeutic objective, but only when the relationship between drug concentration and drug effect is understood.

Figure 3-21 Fentanyl and alfentanil arterial concentrations (circles) and electroencephalographic (EEG) response (irregular line) to an intravenous infusion. With each drug, there is a time lag between the rise and fall in arterial concentration and the EEG response, but the time lag is much greater for fentanyl than for alfentanil. (Adapted from Scott JC, Ponganis KV, Stanski DR: EEG quantitation of narcotic effect: The comparative pharmacodynamics of fentanyl and alfentanil. Anesthesiology 62:234–241, 1985.)