Fluidized Bed Coating Technique for Production of Sustained Release Granules

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Abstract
A laboratory-scale instrument for fluid-bed spray coating of granules has been constructed. Its major advantage is its suitability for development work on small batches of granules or tablets of between 50 and 300 grams. Commercial equipment available at present requires minimum loadings of 0.5-1 Kg. for effective operation. The instrument has been successfully used for producing sustained-release products by coating granules of model drugs with EC, and data are presented which define important qualities of the products. In particular, the apparatus is capable of giving excellent batch homogeneity and reproducibility. One of the recent successful developments in pharmaceutical technology is the production of sustained-release dosage forms. The two main approaches utilized in the design of these products are (a) the introduction of a physical barrier preventing contact between the drug and the fluids of the digestive system, the effect of which is to reduce the rate of diffusion or leaching out of the drug from the dosage form (b) the addition of selected interactants to the formulation, such as ion-exchange resins or complexants, which form weak cnemical bonds with the drug. The present work is concerned with the first type of product which in practice may be produced using widely different technologies. The main ones are based on (a) coating techniques (b) embedding the drug in a wax or polymer matrix. Prior to 1956, coating was performed by means of the classical rotating pan-method, but in that year Spaulding (1) introduced a controlled spray technique for application of the coating solution to the pan contents, termed the rotating pan-spray technique. A new and major step in coating technology was the introduction into pharmaceutical manufacturing of the fluidized-bed technique. The term “fluidized-bed” has been defined in a number of ways (2-4); most simply, when a solid is “fluidized” in a process, it shows in its behaviour many of the physical characteristics of a liquid. In pharmaceutical production, fluidization methods are utilized in stages of drying (5-6), granulation (7) and coating (8-9). As a coating technique, its main advantages over the pan-coating method are as follows: a) irregular particles may be coated directly, b) loss of material is small, c) the process may be automated and does not require learning the “art” of coating, d) it is very rapid. The present work is a study of the preparation of sustained-release granules coated by means of the fluid-bed technique. Salicylic acid and caffeine were selected as model drugs, while ethyl cellulose (EC) with polyethylene glycol (PEG) were representative of coating materials.

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