Hosting of the antibiotic Vancomycin by bentonite: Characterization and slow release study

Abstract Bentonite (Bent) is a highly promising material to be used in the pharmaceutical industry as drug delivery system due to its high drug loading capacity and controlled drug release properties. The adsorption and controlled release of vancomycin (VCM) ―a glycopeptide antibiotic of large molecular size and structural complexity― on/from an unmodified Bent is reported. The adsorption and release of this drug on/from the Bent―whose safety was demonstrated by in vivo studies―was monitored by ultraviolet (UV) spectroscopy. In order to enhance the VCM loading by the clay, different physical-chemical parameters (pH, drug initial concentration, temperature and interaction time) were evaluated. The Bent-VCM composite was characterized by X-ray diffraction (XRD), transmittance Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The results showed that the Bent is able to efficiently adsorb VCM, achieving a higher load (qmax= 655 ± 5 mg/g) at 9 × 103 mg/L, when it is in its monovalent cationic form. The characterization studies indicated surface adsorption, as well as clay-drug interactions by hydrogen bridges and electrostatic forces. The Sips isotherm model exhibited a good correlation to the equilibrium experimental data, indicating heterogeneous adsorption of the adsorbate-adsorbent system under study. The ΔG0 calculation indicated the spontaneous and reversible nature of the adsorption process. The in vitro assays at pH values typical of the human gastrointestinal tract demonstrated that the VCM release profiles fulfill the pharmaceutical standards, suggesting the potential use of Bent as VCM carrier.