ction sites according to distribution volume. In general
terms, three types of receptors can be differentiated:
those located within the cell, such as CYT P450, which
is located within the microsomes; those located external
to and within the cell membranes, such as the potassium
and calcium channels; and fi nally the so-called surface
receptors, such as the 5-HT and H1
receptors. The H1
receptors are widely distributed throughout the body,
and are found in smooth muscle, endothelial and
epithelial cells, eosinophils or neurons. A suffi ciently
low distribution volume means that the intracellular
receptors remain unaffected. Taking into account that the
H1
receptors are easily accessible from the bloodstream,
the H1
antihistamines do not require extensive tissue
distribution for correct action. The advantages of a low
distribution volume include minimum dose-dependent
toxicity for cell and organs, minimum interindividual