Utility of nuclear magnetic resonance spectroscopy to characterize the structure of dexamethasone sodium phosphate inclusion complexes with cyclodextrins in solution and to analyze potential competitive effects

Abstract

The interaction between dexamethasone sodium phosphate (DSP) and four cyclodextrin (CyD) derivatives [2,6-di-O-b-cyclodextrin (DIMEB), g-cyclodextrin (g-CyD), and hydroxypropyl-b-cyclodextrin with either 2.7 or 4.6 degrees of substitution (HPbCyD 2.7 and HPbCyD 4.6, respectively)] was investigated by proton nuclear magnetic resonance spectroscopy (1H NMR). The data suggested the formation of inclusion complexes in solution in which B andC rings ofthe moleculeare located inside the cavity. Nevertheless, the structure, in terms of depth within CyD, depends on the derivative considered. Molecular mechanics calculations of DSPcomplexes withDIMEB and g-CyD support the NMR results. The potential displacement of DSP from the CyD cavity by usual ophthalmic drugs (e.g., polymyxin B, trimethoprim, and benzalkonium chloride) was determined by NMR. The technique has been found useful to analyze this problem in pharmaceutical preparations