An easy and general method for quantifying Azithromycin dihydrate in a matrix of amorphous Azithromycin

Abstract

Azithromycin is a macrolide antibiotic with several important advantages over the parent drug, erythromycin A, such as a wider spectrum of activity, better bioavailability and pharmacological and pharmacokinetic properties, which has a crystalline form and several patented pseudopolymorphs. There are also amorphous forms which show remarkable advantages over the known crystalline forms, but spontaneously produce the dihydrate under some particular conditions. The amount of crystalline phase is usually below 10% and typically 3-5%. We report a new procedure for directly and easily quantifying the crystalline dihydrate form in samples of amorphous Azithromycin by using the X-ray diffraction pattern of the mixture and combining the most intense peak of the dihydrate and an estimation of the background, which gives a good linear relationship between the percentage of crystalline phase and the area of the main peak. ©ARKAT.