Thermal and spectral characterization of a binary mixture (acyclovir and fluocinolone acetonide): Eutectic reaction and inclusion complexes with β-cyclodextrin

• DSC, FT-IR and HSM measurements for the (ACV–FA) system.
• Solid–solid transitions for the pure compounds.
• Eutectic reaction followed by decomposition.
• Inclusion complexes in solid state and aqueous medium with β-CD.

The thermal and structural properties of acyclovir (ACV) and fluocinolone acetonide (FA) have been studied alone and in the corresponding binary mixture, using differential scanning calorimetry (DSC), hot stage microscopy (HSM) and Fourier Transform Infrared spectroscopy (FT-IR).The temperatures and enthalpies of solid–solid transitions and melting for the pure compounds were obtained from the DSC data. The predominant crystalline or amorphous character of pure compounds was noticed by HSM experiments and the characteristics absorption bands were obtained using FT-IR spectroscopy.For the binary mixtures, a eutectic reaction was observed in all DSC curves at 526 K, followed by decomposition, a phenomenon that was confirmed by FT-IR measurements. The phase diagram and Tamman's plot suggest a eutectic composition at xACV = 0.80. From the DSC curves and FT-IR spectra obtained for the mixtures of active principle ingredients (APIs) with β-CD we concluded that the inclusion complexes formation takes place for 1:1 mole ratio.