Solution-mediated crystallization of amorphous azithromycin.

Water and water vapor are the bane of amorphous drug stability, both in storage and after administration. As is to be expected, crystallization of amorphous azithromycin did occur when exposed to water as dissolution medium. However, experimental results showed that, although solution-mediated phase transformation had occurred, it was not a rapid process for this drug. It is considered to be an advantageous characteristic of amorphous azithromycin and likely due to the high molecular mass (748.984 g/mol) and complex structure necessitating more energy for transformations to occur. A high apparent solubility is maintained for a considerable period of time, potentially rendering a higher percentage of this BCS Class II drug available for absorption when administered orally.