Tablets & Capsules

TC0416

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eye on During tablet and capsule manu- facture, fumed silica prevents powder formulations from building up along the walls of hoppers. That, in turn, prevents irregular flow, agglomera- tion, and segregation, all of which impair productivity and quality. Its Table 1 Correlation of angle of repose to powder flowability Angle of repose Flowability (degrees) 25-30 Very free flowing 30-38 Free flowing 38-45 Fair/passable flow 45-55 Cohesive >55 Very cohesive Source: Bodhmage, A. (2006). Correlation between physical properties and flowability indicators for fine powders. Unpublished doctoral dissertation, University of Saskatchewan. properties also ensure the powder flows as it should into the dies on the tablet press and/or into capsules, pre- venting the API from segregating from the excipients, which could cre- ate content uniformity issues and off- spec weights. Fumed silica also helps particles rearrange as they fill the die and during the early stages of com- pression, which enables them to form strong bonds to one another. Strong bonds prevent or reduce broken or chipped tablets, capping, and lamina- tion. Fumed silica can also help in the spray drying process. Powder flow Angle of repose provides a useful correlation to powder flow proper- ties. See Table 1. To demonstrate how fumed silica improves flow, it was tested at differ- Tablets & Capsules April 2016 47 Elizabeth Sims and Michael Famiglietti Cabot Corp. excipients This edition of the column—a follow-up to John McCarty's three-part series on using silica in pharmaceutical solid dosage forms—focuses on Cab-O-Sil M-5P fumed silica [1, 2]. It cites the results of several laboratory tests to demonstrate how the excipient makes powder formulations flow better, thus improving tablet quality and manufac- turability. M-5P fumed silica is a high-purity excipient classified as a flow aid and glidant. It has a surface area of 200 square meters per gram and a bulk density of less than 60 grams per liter. Its main function is to improve the flow of pharmaceutical powders and dietary supplements. It does this in three ways. It can act as a "spacer" between particles in the powder for- mulation, thereby reducing the attraction between particles and allowing the powder to flow more easily and clump less. Hydrophilic fumed silica can also act as a "sponge," absorbing moisture that would otherwise create liquid bridges between powder particles. This also improves powder flow. Last, fumed silica particles easily develop a nega- tive electrostatic charge through fric- tion (triboelectricity), creating a repulsive force between powder par- ticles. That minimizes interaction between the particles, thus promot- ing powder flow. Figure 1 Effect of M-5P fumed silica on the flowability of APAP, ibuprofen, and aspirin formulations at different use levels 55 50 45 40 35 30 25 0 0.25 0.45 0.75 Cohesive APAP Ibuprofen Aspirin Fair/ passable flow Free flowing Very free flowing Angle of repose Usage level of M-5P fumed silica (weight %)

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