Characterization of Azithromycin hydrates

Azithromycin (AZI) is a macrolide antibiotic with an expanded spectrum of activity that is commercially available as a dihydrate. This study was carried out to characterize hydrates of azithromycin. A commercial dihydrate sample was used to prepare monohydrate from water/ethanol (1:1) mixture. Hydrates were characterized using DSC, TGA, KFT, XRD, HSM, SEM and FT-IR. TGA showed that the commercial samples are dihydrate and the sample prepared from water/ethanol (1:1) was a monohydrate. Solubility studies revealed that monohydrate converted to dihydrate during solubility studies and as a result there was no significant difference in the equilibrium solubility of MH and DH. Thermal analysis under various conditions revealed that dehydration and melting took place simultaneously. Anhydrous AZI was found to be hygroscopic and converted to DH on storing at room temperature. Molecular modeling studies revealed the probable sites of attachment of water molecules to AZI.