A well established and rapidly growing process, spray drying is the continuous transformation of feed from a fluid state into dried particulate form by spraying the feed into a hot drying medium. The process involves a liquid stream that is continuously atomised, forming very fine droplets, which then enter into a chamber where they are mixed with a hot drying gas, leaving dried solids. The dried powder is then separated from the gas and collected.
The technique is a useful particle engineering tool to modulate the micromeritics and stability of amorphous pharmaceutical materials. Often, spray-dried dispersions are used to improve the solubility and bioavailability of poorly soluble active pharmaceutical ingredients (APIs), supporting proof-of-concept studies. The dispersions are also used for the continuous production of dry solids in powder, granulate or agglomerate form from liquid feedstocks as solutions, emulsions and pumpable suspensions, and to inhibit the crystallisation of a drug in solution.
As a flexible process that provides a high level of control over particle size and molecular characteristics, spray drying can easily manipulate powder or particle attributes such as size, morphology, density and the level of residual solvents. The process is applicable to excipients, APIs or finished drug products, as well as a broad range of physiochemical properties in a variety of powder formulations and advanced solid forms. It can also be applied to temperature-sensitive compounds and materials that are hard to crystallise. In addition, spray drying can achieve controlled release, taste-masking and advanced powders with increased bioavailability.
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