The pharmacokinetics of drugs vary markedly among patients. It is also necessary to aware that pharmacokinetics can change within the same patient. A typical example is drug interactions. Psychotropic drugs generally have a high plasma protein binding rate, which may increase the effects of medications taken concomitantly. Furthermore, psychotropic drugs often competitively inhibit the enzymes metabolizing drugs, and thereby increase the blood levels of concomitantly administered medications. On the contrary, there are also psychotropic drugs, which induce metabolic enzymes and thereby lower the blood levels of concomitant medications. As the number of drugs administered increases, these interactions become more complicated, creating increasing difficulty in estimating clinical effects. Therefore, multi-drug combination therapy is not, based on pharmacokinetic considerations, recommended.
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