Crystal Structure of Levofloxacin Anhydrates: A High-Temperature Powder X-ray Diffraction Study Versus Crystal Structure Prediction

Abstract

Levofloxacin, the levo-isomer of the antibiotic ofloxacin, can crystallize into two different hydrate forms, the monohydrate and the hemihydrate. Although these forms are well characterized, little is known about their anhydrous structures besides the study of Singh and Thakur using crystal structure prediction. In order to solve this issue, this paper proposes the use of high-temperature powder X-ray diffraction to determine the anhydrous structures of the levofloxacin forms termed in the literature as α and γ, herein obtained by heating of the levofloxacin monohydrate and hemihydrate, respectively. These are the first levofloxacin anhydrates whose structures could be solved. To support our results, the dehydration process has been also evaluated by means of differential scanning calorimetry, thermogravimetric analysis, and hot-stage polarized microscopy. The resulting X-ray structures differ from the ones reported as the best-predicted solution, although the predicted work had predicted similar structur...