[Therapeutic drug monitoring with the help of serum concentration measurements. How are the analytic results distributed in a population?].

Therapeutic drug monitoring includes measurement of serum concentrations of drugs when this is possible and appropriate. A therapeutic range is defined for populations where the serum levels represent an optimal relationship between clinical effects and side effects for most of the individuals in the population. Compared with the rest of the population, some individuals are atypical, both with respect to response to and elimination of drugs. Therapeutic drug monitoring makes individualization of dosages in these individuals easier, but often requires extra effort. Compilation of serum level measurements for different drugs for a period of six months showed that the tailoring of digitoxin, carbamazepine, lithium and phenobarbital is as close to optimal as can be expected for a population. For amitriptyline, digoxin and theophylline, a considerable increase in clinical effect within a population of users could probably be achieved by bringing more individual serum levels from the subtherapeutic into the therapeutic range. Nor does the therapeutic potential of phenytoin, nortriptyline and valproate seem to be fully utilized.