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LENNART K. PAALZOW AN. R. ACAD. NAC. FARM.

DRUG DOSING TODAY

When the physician has decided to prescribe a specific drug she
or he has to recommend a certain dose and dosing interval. Usually
the doctor chooses the average dose found in the physician desk
reference. Then she or he changes the dose by trial and error. In
certain cases, although not very common, the prescribed dose is
based on the gender, bodyweight and age. For certain drug excreted
by the renal route, the kidney function is taken into consideration
when chosen the dose.

The most common way of adjusting or prescribing the dose is
based on how the patient reacts on the given drug and acordingly
changed next time the patient meets the physician. In some few
instances the dose is selected based on laboratory finding and finally
for some drugs it is based on the measurements of drug concentra-
tion in the blood or plasma.

There are estimations reported that for certain drugs only about
half of the patients get the correct dose and the 50% of the patients
doses (5). However, by measuring the blood concentration and the
use of the knowledge we have in pharmacokinetics we have today
the possibility to decide about the dose and individual patient should
take in order to get an optimal therapeutic effect. So the question is:
Should we give the same dose to all individuals or after the specific
need of the individual patient?

During recent years it has been an ongoing discussion that in the
future the dose of a drug should be selected based on the genetic
constitution of the patient. Examples of inherited variability in phar-
macokinetics have so far been almost exclusively restricted to drug
metabolism. By performing phenotyping or genotyping we have been
able to characterize rare phenotypes. Despite its appeal, metabolite
phenotyping is not widely employed in clinical practice while geno-
typing holds the promise of providing a more direct approach toward
predicting metabolic phenotypes. However, we have to remember
that pharmacokinetics parameters like volume of distribution, renal
excretion and absorption most probably are not under genetic con-
trol and additionally, the behavior of a drug in the body are influen-
ced by a number of physiological factors like drug binding, blood

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