Spray Drying and Pharmaceutical Applications

Pharmaceutical Technologies International, Inc., Belle Mead, New jersey, U.S.A. Susan C. Wendel 

The first detailed description of the drying of products in spray form was mentioned in a patent of 1872 entitled Improvement of Drying and Concentration of Liquid Substances by Atomizing (2). However, this process found its first significant applications in the milk and detergent industries in the 1920 s (3). In current times, spray drying is utilized extensively in many aspects of our daily life from food products, cosmetics, and pharmaceuticals to chemicals, fabrics, and electronics. Typical pharmaceutical examples include spray-dried enzymes (such as amylase, protease, lipase, and trypsin), antibiotics (such as sulfathiazole, streptomycin, penicillin, and tetracycline) and many other active pharmaceutical ingredients, vitamins (such as ascorbic acid and vitamin B12), and excipients for direct compression (such as lactose, mannitol, and microcrystalline cellulose). 

There are several reasons why the technology of spray drying has found many applications in numerous industries. It is a continuous process. As long as liquid feed can continue to be supplied to the drying system the spray-dried product will continue to be produced. In some instances, this process has been operated for months without interruption. The physical properties of the resulting product (such as particle size 

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The advent of biotechnology, bioengineering and pharmaceutical delivery systems has increased the requirements for solubility and stability of macromolecules under a variety of versatile and unique conditions and subsequently the use of non-aqueous solvents. Specihc applications include a) isolation, purification, precipitation and crystallization of biopharmaceuticals, b) processing methods such as spray drying and microencapsulation, and c) formulation of proteins for delivery systems requiring high concentrations and prolonged stability, such as implants and depots. 

Because of its inherent costs, spray drying is not always considered as a processing option for many conventional formulations. However, when a specialized particle type is required by the active ingredient or dosage form, spray drying can become a feasible alternative to more conventional manufacturing processes. Such particle types include microcapsules, controlled release particles, nanoparticles, and liposomes. The application of spray drying to pharmaceuticals has been extensively discussed in review articles (21,22). 

Microcrystalline Cellulose. Microcrystalline cellulose is a purified, partially depolymerized cellulose that occurs as a white, odorless, tasteless, crystalline powder composed of porous particles. It is widely used in pharmaceutical dosage forms, primarily as a filler-binder in oral tablets and capsules with both wet granulation and direct compression processes. Microcrystalline cellulose was marketed first in 1964 by the FMC Corporation under name Avicel PH in four different particle size grades, each with different properties.37 Addition of Avicel into a spray-dried lactose-based formulation overcame compressibility problems. At the same time, the lactose enhanced the flowability of the Avicel products available at that time. The direct compression tableting process became a reality, rather than a concept, partially because of the availability of Avicel. As of 2007, Avicel PH is commercially available in 10 types with different particle size, density, and moisture grades that have different properties and applications (Table 7.6).38 Other brands of microcrystalline cellulose are also available on the pharmaceutical market, including Pharmacel 101 and 102 from DMV International and Emcocel 50 M and 90 M from JRS Pharma. 

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