Changes in Melting Time of Suppositories
Suppositories are designed to melt after rectal administration, and this process is crucial to the release of active ingredients. If storage results in hardening of the suppositories such that the time required for them to melt is prolonged, this could result in an inferior product. As shown in Fig. 175, long-term storage of some products, even at 20°C, resulted in a prolongation of melting times.707 708 The hardening effect increased with increased storage temperature up to 25°C but decreased at higher temperatures owing to partial melting of the suppository base (Fig. 176). Thus, in this case, accelerated testing at a higher temperature would not have been useful.
Many suppository bases are made up of various acylglycerols. Hardening of suppositories is considered to result from various phase transitions, crystallization, and transesterifi-cation reactions in these lipids. The DSC thermograms of a semisynthetic, hard base triglyceride shown in Fig. 177 indicate that a polymorphc phase transition occurred during storage.709
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