Differential scanning calorimetry.
The thermal properties of the drug, myrj-52, PM, SD, and granules prepared by melt granulation were studied using DSC (see
Figure 4). Meloxicam shows a sharp melting endothem at 258.1 °C. The exothermic peak after the melting peak may be part of
the decomposition peaks also observed by Cantera et al. in tenoxicam (13). Thin-layer chromatography of meloxicam melted at
265 °C on an oil bath showed two different bands, which indicate the decomposition of the drug in melt form. The color of
drug after melting at 265 °C also changed from yellow to reddish brown. Slow, controlled heating of the drug in DSC did not
yield two separate peaks for melting and decomposition. DSC of pure myrj-52 showed an endothermic peak at 51 °C. The thermogram
of pure StarLac showed endothermic peaks at 150 and 215 °C for starch and lactose, respectively. The thermogram of physical
mixture with myrj-52 showed endothermic peaks at 49.9, 103.9, 216, and 231 °C, corresponding to myrj-52, starch, lactose,
and meloxicam, respectively. Normalized enthalpics of PM, SD, and MG samples were lower (i.e., 63.8, 77.0, and 61.2 J/g, respectively)
compared with pure meloxicam (338.1 J/g).
Figure 4: Differential scanning calorimetry curves 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.
The shift and breadth of the endothermic peak probably results from the partial reduction in crystallinity, which may be confirmed
in PXRD studies.
Powder X-ray diffractometry.
The authors performed PXRD analysis to confirm the crystalline nature of meloxicam in the granules. The numerous sharp and
intense peaks in the diffractrogram of untreated meloxicam shows that the drug is crystalline.
PXRD of meloxicam showed characteristic peaks at 13°, 14.5°, 18.5°, and 26°. Peaks at 26° were used to compare the PXRD pattern
of the drug with those of PM, MG, and SD (see Figure 5). A significant reduction in peak intensities was observed in the PXRD
patterns of PM, MG, and SD compared with that of the pure drug. The PXRD pattern of myrj-52 showed two typical peaks in the
region of 19.5° and 24°. The PXRD patterns of PM, MG, and SD showed all of meloxicam's peaks except for the peak at 26°. The
disappearance of the peak at 26° in the patterns of PM, SD, and MG might result from an attenuation of the signal in the presence
of excipients or preferential orientation.
Figure 5: X-ray diffraction pattern 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.
The traces of PM, MG, and SD are similar to each other. The characteristic peaks of the drug are always present, indicating
that meloxicam is crystalline in PM, MG, and SD samples. Therefore, X-ray data confirm that the enhanced dissolution rate
of the drug does not result from the transformation of the crystalline form into the amorphous state.