Inclusion Complex of Carprofen with Hydroxypropyl-β-cyclodextrin

The aim of this study was to investigate the characteristics of hydroxypropyl-β-cyclodextrin (HPCD) on the solubility, photostability and dissolution of carprofen (CP). It was found that the solubility of carprofen increased 52-fold when 16% HPCD was added to H₂O (w/v). The phase-solubility diagram revealed the formation of a 1:1 inclusion complex of CP-HPCD with a stability constant (k_s) of 487 M^-1. Formation of the inclusion complex of CP-HPCD was analyzed using differential scanning calorimetry (DSC). Changes in chemical shifts of the ¹H-nuclear magnetic resonance spectra of CP-HPCD demonstrated that the inclusion site of CP by HPCD was carbazolyl aromatic ring skeleton rather than the side chain of propanoic acid. The photostability study revealed that the CP-HPCD complex could not significantly decrease the rate of photodegradation of CP, implying that the rate-determining step of CP mainly occurred at the side chain. The dissolution rates of CP were significantly enhanced as the proportions of HPCD increased in the prepared discs. The dissolution of the physical mixture (in a 1:3 molar ratio) increased by about 6-fold in comparison with the parent drug. The improvement of wettability and solubility of CP by complexing to HPCD was reflected in the enhanced dissolution rate.