Preparation of amorphous indomethacin from aqueous 2,6-di-O-methyl-β-cyclodextrin solution

Indomethacin precipitated exclusively in an amorphous form from aqueous 2,6-di-O-methyl-β-cyclodextrin solutions, whereas it precipitated in Form V polymorph from the solutions of the drug alone, parent cyclodextrins and 2-hydroxypropyl-cyclodextrins. The polymorphic transition of the amorphous form to Form V crystals in aqueous solution was markedly inhibited by the addition of 2,6-di-O-methyl-β-cyclodextrin, keeping the amorphous state for at least 5 days at 4 °C, whereas it quickly transformed to Form V crystals in the absence of 2,6-di-O-methyl-β-cyclodextrin. 2,6-Di-O-methyl-β-cyclodextrin suppressed the solution-mediated polymorphic transition of amorphous form of indomethacin to Form V crystals in aqueous solution. The current results suggested that 2,6-di-O-methyl-β-cyclodextrin is useful for isolation of amorphous indomethacin that occurs at an early stage of crystallization according to “Ostwald's Rule of Stages”.