3 The biopharmaceutical classification system (BCS) categorizes oral medications into four groups on the basis of their solubility and permeability characteristics.4 The use of pro-drugs, salt formation, and micronization, preparation of solid dispersions with soluble polymers or conversion of the crystalline drug to the amorphous form have all been suggested and used. The drug can be dispersed molecularly in amorphous particles (clusters) or in crystalline particles.5 The amorphous state is characterized Vorinostat by the absence of the long-range, three-dimensional molecular order characteristic of the crystalline state. From a practical standpoint,

an amorphous material can be obtained in two ways: (i) by cooling the molten liquid until the molecular mobility is “frozen in,” thus producing the glass and (ii) by gradually inducing defects in the crystal until the amorphous form is attained. At industrial scale amorphous solid dispersions can be prepared by processes such as fusion method, rapid solvent evaporation method (spray drying, vacuum drying, freeze drying) and spray congealing method. However, they may not be amenable to conventional ABT-199 clinical trial dosage form manufacturing processes due to the typical soft, tacky nature and sensitivity to stress as a trigger for instability. The salient features for design of solid dispersions would include judicious selection of carrier,

drug-carrier ratio and understanding the drug release mechanism from matrix. The thermal, chemical and mechanical stress applied during processing can spontaneously induce the recrystallization process. In the changing paradigm of drug discovery, amorphization of drug provides an attractive option for overcoming solubility limitations for ‘difficult to deliver’ drugs. Accompanied with a molecular level understanding of amorphous systems, we can design systems

with predictable stability and performance. Of these approaches, amorphous materials are attractive as they are broadly applicable Liothyronine Sodium and fit the generic criteria established for good formulation approaches.6 ASD is broadly applicable to acidic, basic, neutral, and zwitterionic drugs.7 The characterization of amorphous solids differs from that for crystalline solids. It is customary to characterize an amorphous material both below and above the glass transition temperature, i.e., both as the frozen solid and as the supercooled viscous liquid. The physical characterization of amorphous solids utilizes a wide range of techniques and offers several types of information.15 Powder X-ray diffraction can be used to qualitatively detect material with long-range order.16 Sharper diffraction peaks indicate more crystalline material. Diffraction techniques are perhaps the most definitive method of detecting and quantifying molecular order in any system, and conventional, wide-angle and small-angle diffraction techniques have all been used to study order in systems of pharmaceutical relevance.