[Pharmacokinetic factors and resistance to antidepressant treatment]

A number of treatment failures occurring during antidepressant treatment may be related to the pharmacokinetics of the drug used. In fact, numerous factors are able to modify the fate of the antidepressant in the body. These factors may involve the absorption, distribution, biotransformation or elimination of the drug. The reality of these problems is illustrated by a number of clinical case reports. Such modifications lead to a variation in the quantity of drug available to exert its antidepressant action at the sites responsible for the pharmacodynamic effects. This raises the possible value of defining, and then using in practice, the therapeutic zone of the plasma concentrations of the antidepressant used, below and above which a poor therapeutic response is likely. Modern analytical techniques actually allow the routine analysis of plasma concentrations of a number of antidepressants, resulting in a more rational approach to drug therapy and a decrease in the number of depressions resistant to antidepressant treatments.