Wettability and surface chemistry of crystalline and amorphous forms of a poorly water soluble drug

The present study compares energetics of wetting behavior of crystalline and amorphous forms of a poorly water soluble drug, celecoxib (CLB) and attempts to correlate it to their surface molecular environment. Wettability and surface free energy were determined using sessile drop contact angle technique and water vapor sorption energetics was measured by adsorption calorimetry. The surface chemistry was elucidated by X-ray photoelectron spectroscopy (XPS) and crystallographic evaluation. The two solid forms displayed distinctly different wetting with various probe liquids and in vitro dissolution media. The crystalline form surface primarily exhibited dispersive surface energy (47.3 mJ/m2), while the amorphous form had a slightly reduced dispersive (45.2 mJ/m2) and a small additional polar (4.8 mJ/m2) surface energy. Calorimetric measurements, revealed the amorphous form to possess a noticeably high differential heat of absorption, suggesting hydrogen bond interactions between its polar energetic sites and water molecules. Conversely, the crystalline CLB form was found to be inert to water vapor sorption. The relatively higher surface polarity of the amorphous form could be linked to its greater oxygen-to-fluorine surface concentration ratio of 1.27 (cf. 0.62 for crystalline CLB), as determined by XPS. The crystallographic studies of the preferred cleavage plane (0 2 0) of crystalline CLB further supported its higher hydrophobicity. In conclusion, the crystalline and amorphous forms of CLB exhibited disparate surface milieu, which in turn can have implications on the surface mediated events

Impact of Crystal Habit on Biopharmaceutical Performance of Celecoxib

Poor biopharmaceutical performance of Biopharmaceutical Classification System (BCS) class II drug molecules is a major hurdle in the design and development of pharmaceutical formulations. Anisotropic surface chemistry of different facets in crystalline material affects physicochemical properties, such as wettability, of drugs. In the present investigation, a molecule-centered approach is presented toward crystal habit modification of celecoxib (CEL) and its effect on oral bioavailability. Two crystal habits of CEL, acicular crystal habit (CEL-A) and a plate-shaped crystal habit (CEL-P), were obtained by recrystallization from toluene at 25 and 60 °C, respectively. Compared to CEL-A, CEL-P exhibited significantly faster dissolution kinetics in aqueous media and significantly higher <i>C</i>_max and shorter <i>T</i>_max in an oral bioavailability study. The significant enhancement in dissolution and biopharmaceutical performance of CEL-P was attributed to its more abundant hydrophilic surfaces compared to CEL-A. This conclusion was supported by wettability and surface free energy determination from contact angle measurements and surface chemistry determination by X-ray photoelectron spectroscopy (XPS), crystal structure modeling, and crystal face indexation