Polymorphic transition rate of semisynthetic fatty suppository bases.

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Abstract
The degree of polymorphic transition of semisynthetic fatty suppository bases was estimated by means of X-ray diffraction measurements. IR values, defined as the relative intensities of 2 characteristic diffraction peaks of unstable A-form and stable B-form were used. Storage experiments using Witepsol H-15 suppositories containing Brilliant Blue were performed. During storage the changes of melting point, softening time and drug release rate were measured and compared with IR. Each of these properties showed a correlation with IR value irrespective of storage temperature or period. With lapse of time the IR values commonly fell to a minimum in the earlier period, subsequently increased to a maximum and then remained constant. This change depended markedly on the storage temperature; the IR change was predicted using 2 rate parameters: the half-transition time t1/2 and the shift factor AT calculated by the reduced variable method. On plotting these rate parameters against 1/T, good linear relations were obtained and the activation energies were 98 kcal and 108 kcal for t1/2 and AT, respectively. Using these values, the physical stability of the suppository can be predicted. This IR method is applicable to other commercial fatty vehicles.

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