Pharmacokinetics can be defined as the study of the fate of drugs in the body or as the study of the influence of the body on drugs. The body usually reacts to an exogenous molecule by reducing its absorption, by converting it into inactive metabolites and by eliminating it. Pharmacodynamics is the study of the effects of drugs,
The aim of pharmacokinetics is to provide the knowledge necessary to understand how to adjust the dosage of a drug to obtain the plasma concentration inducing the optimum effect, i.e. the best efficacy with the minimum of adverse effects. At too low concentrations, the drug is ineffective and at too high concentrations, its adverse effects become too important compared to its efficacy.
In clinical pharmacology, the only directly accessible parameter is the concentration of drugs in plasma. All pharmacokinetics is based on the variations of plasma concentrations. The pharmacokinetic differences between drugs result primarily from their facility to cross biological membranes and from the rate of their inactivation.
The acquisition of a basic pharmacokinetic knowledge necessary for a correct prescription does not require any particular mathematical competence.
We successively study
- Definition of the principal parameters used in pharmacokinetics
- Evolution of plasma concentrations of a drug according to the conditions of its administration
- Passage across membranes
- Routes of administration
- Blood and tissue distribution