Effect of Drugs on the Surface Activity of Surfactants in Aqueous Systems.
The effects of some drugs on the surface activity of a cationic, an anionic and a nonionic surfactant have been investigated. Polar drugs, atropine sulphate and phenobarbitone sodium and relatively hydrophobic drugs (sulphadiazine and chloramphenicol) were utilised in the study. The charge on the active principle in the drug governed its interaction with the surfactants. The negatively charged phenobarbitone-moiety enhanced the surface activity of sodium lauryl sulphate while the cationic atropine moiety achieved the same effect with cetrimide. The surface activity of phenobarbitone sodium and atropine sulphate was established and synergism was proved in the interaction of cetrimide and atropine sulphate. The interaction of surfactants with drug moiety of opposite charge did not follow a particular pattern. Enhancement of surface activity as a result of coulombic forces of attraction is observed in the interaction of Sodium lauryl sulphate and atropine while interaction of phenobarbitone sodium and cetrimide led to the formation of surface active complexes at concentrations below the CMC. Ionic surfactants interacted with the hydrophobic drugs resulting in enhancement of surface activity because of Van der Waals forces of attraction between surfactant and drug. The non-ionics-tween 60, 40 and 20 experienced enhanced surface activity in the presence of the polar drugs. Hydrophobic drugs also interacted with the surfactants through their functional groups. The results of the experiments indicate that an increase in hydrophobic chain length of non-ionic surfactants has no effect on the drug surfactant interaction involving the polar and hydrophobic drugs. The presence of free ions and complexes in the drug-ionic surfactant mixture was tested using conductance measurements.