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VOL. 70 (3), 663-679, 2004 PHARMACOKINETICS AND INDIVIDUALIZED DRUG THERAPY

flow, distribution characteristics etc. and not to forget environmen-
tal and patho physiological factors.

THERAPEUTIC DRUG MONITORING (TDM)

As mentioned above the pharmacokinetic science has developed
tremendously but its use in clinical practice has been limited, al-
though it is used widely during drug development by the drug indus-
try. The usage of pharmacokinetics in clinical practice can be called
TDM, therapeutic drug monitoring, which means: To monitor drug
dose and dosing interval by measuring the plasma concentration of
the drug in the individual patient. But in order to use plasma con-
centration for selecting the dose and dosing interval there has to
been a relationship between concentration and therapeutic effects
like for instance the sigmoidal relationships shown in Figure 2 (6).
It may also be inferred that if a substance should become a drug, it
has to be a relationship between dose and effect and if such relatio-
nship exists there is also certainly a relationship between drug con-
centration and effect, even if it in some circumstances can become
somewhat more complex than the relationship shown in Figure 2.

FIGURE 2. The sigmoidal relationship between drug concentration and therapeutic
effects according to a sigmoidal Emax equation.

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