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

CLINICAL INDICATIONS FOR THERAPEUTIC DRUG
MONITORING

When should we monitor drug doses by TDM? In the following
I will give you some examples when TDM are indicated:

• Sometimes it is difficult to judge if lack of therapeutic effect is
due to wrong choice of drug or that other factors could be the
reason to e.g. absence of effects.

• For many drugs it takes time before we can see any effects. For
drugs against e.g psychosis or cancer it may take weeks before
we can say anything about the outcome of the prescribed drug.

• By measuring the plasma concentration we can figure out if
the patient has taken the drug or not.

• For many drugs there is a large variability between patients in
the uptake, distribution and elimination of the drug in the body,
and by measuring plasma concentration we could individualize
the dose.

• TDM should be used for drugs where it is a narrow concentra-
tion range between too low concentration giving no effect and
concentration that are too high and consequently gives side
effects.

• Liver and kidney functions are important for the elimination of
drugs and we have to take their functions in consideration if
they did not function normally.

• Sometimes it is difficult to judge if the patient does not res-
pond to therapy, if this depends on the drug or the illness.

• Quite often we give several drugs simultaneously and in certain
cases could they interact with each other.

• Genetic factors as mentioned above.

DRUGS SUITABLE FOR TDM

From what I have said you may get the impression that all drugs
should be monitored by plasma concentration measurements. That

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