Binding of Sulfamethazine to β-cyclodextrin and Methyl-β-cyclodextrin

beta-cyclodextrin (beta CD) and methyl-beta-cyclodextrin (M beta CD) complexes with sulfamethazine (SMT) were prepared and characterized by different experimental techniques, and the effects of beta CD and M beta CD on drug solubility were assessed via phase-solubility analysis. The phase-solubility diagram for the drug showed an increase in water solubility, with the following affinity constants calculated: 40.4 +/- 0.4 (pH 2.0) and 29.4 +/- 0.4 (pH 8.0) M-1 with beta CD and 56 +/- 1 (water), 39 +/- 3 (pH 2.0) and 39 +/- 5 (pH 8.0) M-1 with M beta CD. According to H-1 NMR and 2D NMR spectroscopy, the complexation mode involved the aromatic ring of SMT included in the M beta CD cavity. The complexes obtained in solid state by freeze drying were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermal analysis. The amorphous complexes obtained in this study may be useful in the preparation of pharmaceutical dosage forms of SMT.