ABSTRACT
Materials processing, often the last stage in a series of unit operations in the pharmaceutical industry, is perhaps the most critical step in drug synthesis. A suitable formulation and an appropriate form of drug delivery to the patient should effectively complement all the multistep operations of drug synthesis. A range of drug delivery systems are available for the administration of medicines, with virtually all requiring drug substances and/or functional formulation constituents in powder form at some stage in their preparation. The tablet, prepared in a variety of types but principally for oral delivery, remains the most popular and widely used form of drug delivery, with the drug mixed and processed with excipient(s) prior to compression into a tablet. Compact strength and hence the drug dissolution rate strongly depend on particle properties. An alternative route of administration for drug delivery that is increasing in interest and use is the respiratory tract (1). For deep lung deposition, the drug is inhaled directly from a metered dose inhaler (MDI) or a dry powder inhaler (DPI) whereupon it acts locally and/or is absorbed into the bloodstream in the lungs. This form of drug delivery generally requires the particle size of the drug in the narrow size range of 1-5 µm to be effective (2). Another class of delivery systems is for modified drug release. In one approach, the drug is trapped in a matrix of a suitable soluble carrier/excipient, and fine tuning the morphological structures of the drug carriers is important in determining and controlling the modified release profile. In another approach, the drug is coformulated along with a polymer to form a solid dispersion. Polymorphic purity is frequently another important issue in pharmacy due to different physicochemical properties and therapeutic effects of the alternative forms (3). Carefully controlled crystallization procedures linked to expensive separation methods are currently employed to obtain pure stable polymorphic forms. The degree of crystallinity of drug substances in powder form is also a critical factor not only in drug stability but also in achieving longevity of final products.
