Pharmacokinetics and Pharmacodynamics
Reference work entry
Pharmacokinetics can be defined as an individual’s response to drug administered (Weinshilboum and Wang 2004). It includes the study of the mechanisms of absorption, action, and excretion of an administered drug. The rate of absorption of drug and the duration of the effect, the chemical changes brought about on the drug molecule in the body, and the rate and routes of excretion of the metabolites of the drug are dynamic parameters studied under pharmacokinetics. These parameters determine the effective concentration of the drug available for action at the target site – referred to as bioavailability. Pharmacokinetics describes the relationship between the drug dose and the resulting drug concentrations in plasma and tissue. It is influenced by variations in drug transport and metabolism (Fig. 1).
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