Enrofloxacin inclusion complexes with cyclodextrins

Inclusion complexes using alpha-, beta-, gamma-, and hydroxypropyl-beta-CD (HP-beta-CD) were produced with the antibiotic enrofloxacin, with the aim of increasing its solubility by complexation. Phase solubility diagrams were obtained, to confirm the formation of inclusion complexes, and to determine the solubility enhancement and stability constant of each complex. Enrofloxacin inclusion in beta-CD showed the highest value of the complex stability constant (35.56 mmol L-1), but the greatest increase in solubility was obtained using HP-beta-CD reaching a 1258% increase over enrofloxacin solubility in the absence of CD. The order of highest enrofloxacin solubility achieved was: HP-beta-CD > alpha-CD > gamma-CD > beta-CD. In addition, formation of complexes was confirmed by differential scanning calorimetry and thermogravimetry, applied to the complexes obtained by the kneading technique. The influence of citric acid, alone or as an adjunct of beta-CD, on the solubility of enrofloxacin was also determined. A solution of 15 mmol L-1 citric acid dissolved 10 g L-1 of enrofloxacin, but a gradual increase in beta-CD concentration in the presence of citric acid did not increase the degree of solubilization of enrofloxacin.