Wettability of a hydrophobic drug by surfactant solutions

Abstract

CI-976 (2,2-dimethyl- N-[2,4,6-trimethoxyphenyl]dodecanamide) was used as a model compound to study the interaction of surfactant solutions with a drug surface because of its high degree of hydrophobicity and low solubility. The advancing contact angles of sessile drops of commonly used surfactant solutions at various concentrations were measured on compressed disks of CI-976 using a contact angle goniometer. In addition, the surface tension of the solutions was measured at 25°C. At surface tensions near 40 mN/m, contact angles ranged from 16° to 65°. Adhesion tension plots for sodium lauryl sulfate and Triton X-100R initially showed near zero slopes at higher surface tensions, then became positive at about 40 mN/m. Tween 80 had a near zero slope over the whole concentration range tested. Calculations of surface energy parameters from contact angles of organic liquids using either two liquids or three liquids show that CI-976 is a low energy solid with surface characteristics similar to that of polymethylmethacrylate. Interaction energies calculated between surfactants and CI-976 correlate with the observed wetting data for the solutions. Dissolution testing of CI-976 powder in gelatin capsules in selected solutions showed large variation in amount dissolved versus time, independent of solubility and in good correlation with contact angle data. The results confirm the importance of wetting in selecting a surfactant for use in dissolution media and demonstrate the utility of contact angle measurements in analyzing wetting of drug substances.