Study on Binding Properties of Poorly Soluble Drug Trimethoprim in Anionic Micellar Solutions

Abstract

Binding and distribution properties of trimethoprim (TMP) in the presence of various anionic surfactants; sodium octyl sulfate (C₈SO₄Na), sodium decyl sulfate (C₁₀SO₄Na), sodium lauryl sulfate (C₁₂SO₄Na), and sodium tetradecyl sulfate (C₁₄SO₄Na) has been studied by conductivity, spectrophotometry and surface tension measurements. The surface properties of anionic surfactants, that is, maximum surface excess concentration (Γ _max ) and minimum area per surfactant molecule (A _min ) at the air/water interface have been evaluated in the absence and presence of TMP using Gibbs adsorption isotherm. From conductivity data the ionization degree and counterion binding parameter have been obtained. Spectrophotometric experiments were used to determine binding constants of TMP to anionic micelles. With the increasing alkyl chain of surfactants, the interaction becomes stronger, which shows the importance of hydrophobic forces and incorporation of TMP molecules to the pure micelles of anionic surfactants increased. The results obtained from the surface tension and conductometric studies have been correlated with those obtained from the spectroscopic studies and binding tendency of TMP to anionic micelles followed the order as: C₁₄SO₄Na > C₁₂SO₄Na > C₁₀SO₄Na > C₈SO₄Na. From these results, the study of the interaction TMP in different anionic micellar solutions provided information about the characteristics of binding properties of poorly soluble drugs.

Keywords:

• Binding constant
• counterion binding parameter
• drug-surfactant interaction
• surface tension
• trimethoprim

Notes

Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/ldis.