Comparison of the Wetting Properties of Three Commonly Used Simulated Intestinal Fluids Used as Dissolution Media in the Characterization of Drugs

Simulated intestinal fluids (SIFs) are described in the United States Pharmacopoeia (USP) and the International Pharmacopoeia (IntPh) as recommended dissolution media for the characterization of solid drugs. This study was carried out to compare their wettability properties. Six different model substrates were used as surrogates for solid drugs. These surrogate solid substrates were characterized by the Lifshitz-van der Waals, electron donor and electron acceptor terms, which are the three components of the total surface energy obtained by the van Oss model, which is based upon Young’s equation. Contact angles of the SIFs on the surrogate solid-substrates were determined dynamically by image analysis up to five minutes after applying a drop of the fluid on the solid surface. Observed time-dependent spreading behavior was accounted for by a linear extrapolation of the experimental data to zero contact time to obtain the apparent equilibrium contact angle at zero time. Additionally, the pH, osmolality and buffer capacity of the SIFs were experimentally determined. Although some differences in osmolality and buffer capacity were observed, no statistically significant differences in the wetting properties of the three SIFs were detected. This confirms recent findings that there are no observed differences in dissolution behavior among these simulated intestinal fluids. Harmonization of these SIFs is thus recommended.