For this reason, in order to fully comprehend the kinetics of a drug it is necessary to have detailed knowledge of a number of factors such as: the properties of the substances that act as excipients, the characteristics of the appropriate biological membranes and the way that substances can cross them, or the characteristics of the enzyme reactions that inactivate the drug.Īll these concepts can be represented through mathematical formulas that have a corresponding graphical representation.
The study of these distinct phases involves the use and manipulation of basic concepts in order to understand the process dynamics.
The two phases of metabolism and excretion can also be grouped together under the title elimination. In rare cases, some drugs irreversibly accumulate in body tissue. Excretion – the removal of the substances from the body.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.Distribution – the dispersion or dissemination of substances throughout the fluids and tissues of the body.Absorption – the process of a substance entering the blood circulation.Liberation – the process of release of a drug from the pharmaceutical formulation.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):
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. Models have been developed to simplify conceptualization of the many processes that take place in the interaction between an organism and a chemical substance. Pharmacokinetic properties of chemicals are affected by the route of administration and the dose of administered drug. by metabolic enzymes such as cytochrome P450 or glucuronosyltransferase enzymes), and the effects and routes of excretion of the metabolites of the drug. 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.
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