<P> Pharmacokinetics describes how the body affects a specific xenobiotic / chemical after administration through the mechanisms of absorption and distribution, as well as the metabolic changes of the substance in the body (e.g. by metabolic enzymes such as cytochrome P450 or glucuronosyltransferase enzymes), and the effects and routes of excretion of the metabolites of the drug . Pharmacokinetic properties of chemicals are affected by the route of administration and the dose of administered drug . These may affect the absorption rate . </P> <P> Models have been developed to simplify conceptualization of the many processes that take place in the interaction between an organism and a chemical substance . One of these, the multi-compartmental model, is the most commonly used approximations to reality; however, the complexity involved in adding parameters with that modelling approach means that monocompartmental models and above all two compartmental models are the most - frequently used . The various compartments that the model is divided into are commonly referred to as the ADME scheme (also referred to as LADME if liberation is included as a separate step from absorption): </P> <Ul> <Li> Liberation--the process of release of a drug from the pharmaceutical formulation . See also IVIVC . </Li> <Li> Absorption--the process of a substance entering the blood circulation . </Li> <Li> Distribution--the dispersion or dissemination of substances throughout the fluids and tissues of the body . </Li> <Li> Metabolism (or biotransformation, or inactivation)--the recognition by the organism that a foreign substance is present and the irreversible transformation of parent compounds into daughter metabolites . </Li> <Li> Excretion--the removal of the substances from the body . In rare cases, some drugs irreversibly accumulate in body tissue . </Li> </Ul> <Li> Liberation--the process of release of a drug from the pharmaceutical formulation . See also IVIVC . </Li>

What are the elements of the pharmacokinetic phase of drug activity
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