in which So/Ss is the ratio of molar solubility of meloxicam in aqueous solutions of myrj-52 to that of pure water, R is the gas constant, and T is the temperature in Kelvin. Table II presents the obtained values of Gibb's free energy.
Table II: Thermodynamic parameters of the solubility process of meloxicam in myrj-52 and aqueous solution at 25 °C.
The data provide information regarding the increased solubility of meloxicam in the presence of myrj-52. The Gibb's free-energy
values show whether the reaction conditions are favorable or unfavorable for drug solubilization in the aqueous carrier solutions.
Negative Gibb's free energy indicates favorable conditions. Gtr values were negative for myrj-52 at various concentrations, indicating the spontaneous nature of meloxicam solubilization.
The values decreased as myrj-52 concentration increased, demonstrating that the reaction become more favorable as the concentration
of myrj-52 increased.
IR studies were performed to determine the interaction and structural changes of drug and excipients. The IR spectrum of
pure meloxicam showed characteristic peaks at 1620 cm–1 (amide carbonyl), 3290 cm–1 (–N–H stretching of secondary amine), and prominent bands such as 848–570 cm–1 (–CH aromatic ring bending and heteroaromatic), 1043 cm–1 (S=O stretching), and 1456 cm–1 (C=C stretching), as shown in Figure 3. The IR spectrum of myrj-52 showed characteristics peaks at 3600 cm–1 (–OH stretching), 1737 cm–1 (–C=O of ester), and 2893 cm–1 (–C–H stretching).
Figure 3: Fourier transform infrared spectra of pure meloxicam, myrj-52, StarLac, melt granulation (MG) of meloxicam in myrj-52,
physical mixture (PM) of meloxicam in myrj-52, and solid dispersion (SD) of meloxicam in myrj-52.
Characteristic peaks of the drug were also present in the IR spectra of PM, melt granules (MG), and SD with broadening and
reducing intensity. Yet the peak at 3290 cm–1 was significantly suppressed for PM, SD, and MG, compared with pure meloxicam. This result indicates hydrogen bonding between
meloxicam and the excipients.