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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...

Ethambutol (ETB) is a chiral dibasic compound formulated and marketed as the (S,S)-ethambutol dihydrochloride, (S,S)-EDH, to treat tuberculosis. It is administered orally in a solid formulation composed of isoniazid, rifampicin, and pyrazinamide as a fixed-dose combination tablet. Because of its high hygroscopicity, (S,S)-EDH is known for catalyzing the degradation of isoniazid by rifampicin to yield isonicotinyl hydrazone. In order to avoid or even minimize these mutual drug–drug interactions, in this work we have focused on the development of less hygroscopic multicomponent solid forms of ETB. Four salts of this drug, namely, oxalate (ETBOXA), maleate, terephthalate, and trichloroacetate, were prepared via supramolecular synthesis by the slow evaporation method and characterized by X-ray diffraction (single crystal X-ray diffraction, powder X-ray diffraction), spectroscopic (Fourier transform-infrared), and thermal (thermogravimetric analysis, differential scanning calorimetry, hot stage microscopy) tec...

5-Fluorocytosine (5-FC) was investigated for the controlled synthesis of cocrystals by applying the pKa rule. Five cocrystals were designed and developed with adipic, succinic, terephtalic, benzoic, and malic acids, all exhibiting negative ΔpKa values ranging from close to zero up to roughly −1. The synthesized cocrystals were analyzed by single crystal X-ray diffraction, and the observed supramolecular synthons were compared to the reported structures containing 5-FC. In the first four cocrystals, the intermolecular interactions between adjacent 5-FC molecules form two different homodimers showing R22(8) motifs and assembled via complementary N–H···O and N–H···N hydrogen bonds, respectively. However, in the cocrystal with malic acid (ΔpKa = −0.1), an intermediate supramolecular synthon pattern between salts and cocrystals is observed. In this crystal packing, the homodimer of 5-FC molecules held by the N–H···O interactions is preserved, but a new heterodimer is formed between 5-FC and the acid molecule, ...