[Can one adjust the distribution of a drug in an organism to its target sites? The example of antihistaminics (anti-H1) and cetirizine].

When comparing the fate of a drug in the body with the location of its receptors, it appears that a large amount of the administered dosage will never reach these receptors. Thus this large amount is useless in terms of drug efficacy whereas it may generate side of toxic effects in other tissues. An attempt to optimize drug distribution is to limit or even to suppress its useless localisations. This is possible with H1 antagonists as these drugs develop benefic effects in organs which are distinct from those where toxic effects may occur. Cetirizine is an example of choice of this strategy. It is poorly distributed into tissues, especially in heart and liver which favors preferential binding at its target H1 selected receptors.