Adsorption from solution, permeation through cellulose membrane, partition coefficient and surface tension of several antidepressants and phenothiazines.

The physico-chemical properties of several antidepressants were studied in comparison with those of tranquilizing phenothiazines, intending to obtain some information useful to understanding of biopharmaceutical and pharmacological mechanisms of antidepressants. The adsorption isotherms of drug by carbon black (CB) were all observed in Langmuir type. The results suggested that the aromatic rings of drug molecules participate in the adsorption and that there is no special difference in behavior at the surface of CB between antidepressants and phenothiazines. Radii of drug molecule were evaluated by various methods, i. e., r1 from the molecular volume, r2 from the assembled Stuart type molecular model, r3 from the area occupied by one molecule at the surface of CB in the adsorption, and r4 from the apparent diffusion constant in the cellulose membrane permeation, giving a good correlation between r1 and r4. Then the permeation through cellulose membrane was considered to belong to the simple diffusion through small pores. Contrary to such a previous investigation as in the case of barbiturates, there was no clear relationship among the parameters to indicate the hydrophobicity, i.e., the adsorbability onto hydrophobic adsorbent CB, partition coefficient between n-octanol or chloroform and buffer solution, and the surface tension. It was found that both lytic effect of histamine-contraction and inhibitory effect of adrenaline-contraction have relation to the adsorbability onto CB from aqueous solution.