PENETRATION OF CHLOROCYCLIZINE AND AMPICILLIN INTO MIXED PHOSPHOLIPID OLEIC-ACID MONOLAYERS

Surface tension-solution concentration relationships reveal that in spite of the higher efficiency of adsorption displayed by chlorcyclizine relative to ampicillin, the effectiveness of adsorption was superior for the latter. These differences in adsorption behaviour between the two drugs studied have been attributed to the differences in their chemical structure. Chlorcyclizine with its two branched hydrophobic benzyl groups exhibits a higher thermodynamic driving force for adsorption than does ampicillin with its one benzyl group. The penetration of these drugs into phospholipid, oleic acid and their mixed monolayers has been assessed by surface pressure and surface potential measurements. Although more space is required to accommodate penetrating chlorcyclizine molecules in a spread monolayer, their penetration into an oleic acid monolayer is higher than that of ampicillin, and is most probably due to an ionic interaction between the drug cation and the oleic acid carboxylate group. The penetration into phospholipid monolayers (which are highly incompressible) and their mixed monolayers with oleic acid was superior for ampicillin at high solution concentrations. The surface potential data corroborate the surface pressure data, but indicate that the presence of oleic acid molecules in the monolayers exerts an unfavourable dipolar matching on adsorbing drug molecules, the effect being superior in the case of ampicillin.