Physical Stability of Capsules
From Pharmpedia
In the use of capsules one important aspect to be remembered is the physical stability of the capsule shells under varying storage conditions. In hard capsules excessive or low humidity conditions must be avoided as the former tend to soften and the later can make the capsules brittle. The soft gelatin capsule rapidly attains equilibrium with the environmental conditions. However, the nature of thee product encapsulated may have an effect on the capsule shell calling for setting up of physical standards for each product.
A control capsule, containing mineral oil with a gelatin shell having a ratio of dry glycerin: dry gelatin between 0.5 to 1 and water to dry gelatin ratio of 1:1 dried to equilibrium at 20 to 30% relative humidity at 70 to 800F is used as standard. This capsule unprotected by any other method will be only transiently effected by humidities lower than 20% R.H. or temperatures ranging from less than 30F to more than 100F. as soon as extremes of conditions are removed the capsules return to normal form. High humidities of more than 60% RH at 70 to 75F can have lasting effects making the capsules bloated or softer and tackier. The capsules may also get stuck together and it may be difficult to separate them. Increase in temperature beyond 750F alongwith high humidities (>45% RH) may fuse the capsules. capsules containing water soluble liquids are damaged t greater extents than the ones having oleaginous products. It is better to expose newly developed capsules with or without products packed in them to accelerated tests like exposure to 80% RH at room temperature and to 1040F temperatures, in open as well as closed containers, and observe for 15 days. Such tests give a fair idea of likely behaviour under storage conditions that capsules may have to face. Manufacturers generally pack capsules in devices/containers designed to prevent exposure to excessive humidity conditions and advise storage within certain temperature ranges only.
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