| abstract |
The invention relates to a polymorphic form of azithromycin dihydrate (9-desoxo-9a-aza-9a-methyl-9a-homoerythromycin A) showing endothermy in differential scanning calorimetry (DSC) at 139° C, when recorded in an open aluminum crucible at a heating speed of 20° C/minute and showing an endothermy of 143, 7±0.5° C with a fusion heat of 54, 6±1.6 J/g when recorded in a capillary crucible at a heating speed of 10° C/minute. The invention also relates to a method for preparing said polymorphic form of azithromycin dihydrate. According to said method, hygroscopic azithromycin monohydrate is treated with acetone; water at 35-40° C is added; the mixture is then stirred at said temperature and crystals of said polymorph are optionally seeded; water is then added and the mixture is cooled at 5° C. |