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VOL. 70 (3), 663-679, 2004 PHARMACOKINETICS AND INDIVIDUALIZED DRUG THERAPY
graphy and mass-spectrometry. These techniques have given us sensi-
tive and specific methods that are able to measure drug and metabo-
lite concentrations in extremely low concentrations.
When plasma concentrations obtained after given dose of a drug
are measured, plasma is used as a reference tissue to describe what
happens to a drug in the body and since its concentrations change
over time it gives every drug its own characteristic time profile (Figu-
re 1). You can say that the characteristic shape of each plasma con-
centration-time curve is an identity of the drug. It is also well establis-
hed that a drug produces its therapeutic effect within a certain range
of plasma concentration, its therapeutic window or target therapeutic
drug concentration (Figure 1). To describe the plasma concentration-
time curve mathematically we use certain pharmacokinetic parame-
ters and the most important ones are clearance, volume of distri-
bution, absorption rate constant and bioavailability (4). Once these
parameters are known we can calculate the plasma concentration time
profile after single or repeated doses.
FIGURE 1. Plasma concentration-time profile of a drug with its therapeutic window.
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