Water-soluble drugs crystal surface

If has been observed fhaf by adsorbing surfactants onto the crystal surfaces of poorly water-soluble drugs, dissolution rate can be enhanced. Chen et al. " showed that the dissolution rate of Cl-1041, a poorly water-soluble compound, in 0.1 N HCl may be affected by the surfactant Tween 80. The effects of surfactant are complicated, and many factors are involved. Above the CMC of Tween 80, the adsorption of the surfactant onto the crystal surface may inhibit crystal nucleation on the surface, and causes the dissolution rate to increase. By adsorbing a very small amount of poloxamer onto the hydrophobic drug particle surface. 

A surfactant is a surface-active agent that is used to disperse a water-insoluble drug as a colloidal dispersion. Surfactants are used for wetting and to prevent crystal growth in a suspension. Surfactants are used quite extensively in parenteral suspensions for wetting powders and to provide acceptable syringability. They are also used in emulsions and for solubilizing steroids and fat-soluble vitamins. 

Fujiwara T, Ichimura K. 2002. Surface assisted photoalignment control of lyotropic liquid crystals. Part 2. Photopattterning of aqueous solutions of a water soluble anti asthmatic drug as lyotropic liquid crystals. J Mater Chem 12 3387 3391. 

Solid dispersions are often used to enhance water solubility [6, 7]. The melting process causes physical changes in the surface structure of the material, the crystals of the drug suffer destruction, and they turn into an amorphous form. This statement can be justified by the results of differential scanning calorimetry examinations. 

Because of low solubility of the compound in pure water, for the oral administration a suspension in an aqueous solution of hydroxyethylcellulose (0.5 %) was used. The solid state physical parameters (particle size, surface area, amorphicity and crystal modification) and the suspension properties (agglomeration tendency, homogenicity and dissolved part of the drug) had to be investigated. For the intravenous administration, an aqueous solution containing saline, DMSO and PEG 400 was used as formulation. 

The authors examined space-filling models of the two conformers and concluded that the phenolic groups were poorly exposed on the molecular surface. The inaccessibility of the phenolic groups was taken to explain both the low solubility of the drug in water and the absence of hydrogen bonding in either of the two crystal forms. 

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