Abstract
The influence of the liquid phase on the A-to-B transition of semisynthetic fatty suppository vehicles during storage was investigated. The addition of a liquid having a high affinity, such as isopropyl myristate, fatty oil, lauryl alcohol, etc., remarkably accelerated the transition, whereas that of a low affinity liquid had little effect. The transition rate evaluated from the time course of transition degree (kT) increased linearly with the weight fraction ratio of liquid phase (fL) to solid phase (1-fL). The case where liquid phase was produced only from molten vehicle containing no liquid additive was also examined. The relation between kT and fL/(1-fL) was investigated 1) for the transition of Witepsol H-15 in the temperature range from 26 to 32°C, and 2) for several commercial vehicles at 30°C. Linear relations also appeared to hold for both cases. Here, the weight fraction of liquid phase at a given temperature was determined by means of differential scanning calorimetry (DSC). The activation energy of transition (E〓) was compared in the presence and absence of liquid additives. E〓 values of Witepsol H-15 containing 10 and 25% fatty oil were about 40 kcal, less than one-half of that of Witepsol H-15 not containing any liquid additives. The transition mechanism was considered to involve dissolution of the solid A-form in the intervening liquid phase followed by crystallization as solid B-form.
