Tablets & Capsules

TC0417

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L 38 April 2017 Tablets & Capsules testing How leak-proof are your capsules? Chris Freeman and Claire Freeman Ametek Brookfield This article discusses using a texture analyzer to determine the strength of hard and soft capsules. The tests enable you to set spec- ifications and keep out-of-spec products from reaching consumers. eaking gelatin capsules diminish consumer confidence in the product and the manufacturer. To prevent defec- tive capsules from reaching the market, you must develop tests to identify them. One approach is to use a texture analyzer instrument that applies tensile and compressive forces to gelatin capsules to confirm they have sufficient wall strength to withstand external forces during manu- facturing, storage, packaging, and transport. When formulating a capsule drug product, it's impor- tant to know whether the fill—both the API and excipi- ents—is compatible with the gelatin shell, which com- prises a mixture of water-soluble proteins. Any substances that contain aldehydes (e.g., formaldehyde) can cause the gelatin to cross-link, with lysine residue within and between gelatin strands. This stiffens the gelatin structure and slows its disintegration. Learning how a fill will inter- act with the gelatin shell's water content is also impor- tant. A highly hygroscopic fill, for instance, may absorb water from the shell and cause it to become brittle and more prone to breakage. A texture analyzer quantifies the mechanical strength of hard gelatin capsule shells so you can assess how dif- ferent fills affect capsule strength and stability. It does so by imposing controlled mechanical conditions on a sam- ple and then quantifying the resulting behavior. How the samples respond relates directly to their physical charac- teristics and provides a real-life indication of their inter- nal structure. A texture analyzer operates in tension or compression mode and can perform cyclic testing, in which it imposes a deformation action multiple times. The instrument mea- sures load force, usually in grams, and associates it with capsule deformation. The results are then presented in a graphical format as force versus time or as force versus distance. Various textural parameters can be at work dur- ing deformation and it's possible to observe them in the force-deformation curve that the test generates. In the last 40 years, many academic studies that used texture analysis have correlated these behaviors with their senso- rial characteristics. Capsule-loop tensile test Equipping the texture analyzer with a capsule-loop tensile fixture, as shown in the photo above, enables you to compare the mechanical strength of empty capsule shells. In practice, the fixture's two thin rods are inserted into one half of the capsule shell, usually the cap. The Preparing to test the tensile strength of a capsule shell (tensile load versus distance)

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