Carrier-free cholesteric liquid crystal and xerogel of clarithromycin-ascorbic acid with enhanced antimicrobial and antibiofilm activity

Antimicrobial resistance represents a worldwide problem that necessitates the creation of innovative pharmaceutical strategies. In this study, two carrier-free supramolecular systems composed exclusively of clarithromycin (CTY) and ascorbic acid (AA) were developed and characterized: a semi-solid amphotropic cholesteric liquid crystal (CLC) and a xerogel. The CLC gel represents the first report of a spontaneous and stable formation of a cholesteric phase from an antibiotic without additional structuring agents. Rheological studies and polarized light microscopy (PLM) show that the mesophase displayed typical viscoelastic behavior with both lyotropic and thermotropic features and consisted of nanometric particles with moderate uniformity, as confirmed by dynamic light scattering (DLS). The system enhanced the antibacterial activity of CTY. This was reflected in a lower minimum inhibitory concentration (MIC) and in the inhibition of Staphylococcus aureus biofilms, including clinical isolates. These findings highlight its potential use in topical or oral antibiotic formulations. The xerogel showed a lamellar organization, as revealed by the calculation of interplanar distances from the X-ray diffraction pattern and further supported by scanning electron microscopy (SEM). This system offers a novel and simple platform for the formulation of antibiotics.