An investigation into the crystallisation behaviour of an amorphous cryomilled pharmaceutical material above and below the glass transition temperature

The aim of this study was to evaluate the glass transition and recrystallisation of a cryomilled drug, TMC125 (Etravirine), with particular emphasis on assessing the physical stability of the drug above and below the glass transition temperature. DSC (conventional, fast and modulated temperature) and variable temperature ATR–FTIR spectroscopy were employed to monitor the glass transition and crystallisation behaviour of the material. The isothermal crystallisation behaviour was investigated at temperatures below Tg. The humidity-induced crystallisation behaviour of the material was evaluated using dynamic vapour sorption (DVS). The glass transition (99°C) was measured in isolation from the crystallisation process using fast DSC, while ATR–FTIR allowed identification of the polymorph formed on recrystallisation. At a heating rate of 0.2°C/min, the onset temperature of the crystallisation exotherm (67°C) was 32°C below Tg. Evidence is presented for incomplete crystallisation under isothermal conditions. In conclusion, the study has ascertained the crystallisation profile of cryomilled Etravirine under both isothermal and scanning conditions, with the material showing marked physical instability below the measured Tg.