Journal
PHARMACEUTICAL DEVELOPMENT AND TECHNOLOGY
Volume 20, Issue 3, Pages 352-360Publisher
TAYLOR & FRANCIS LTD
DOI: 10.3109/10837450.2013.871027
Keywords
Amorphous; characterization; freeze-drying; polyacrylic acid; recrystallization
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Tolfenamic acid (TA) has been transformed from crystalline to amorphous state through freeze-drying by using varying ratios of polyacrylic acid (PA) at various pH values. The characterization of the films has been carried out using X-ray diffraction, differential scanning calorimetry, Fourier transform infrared (FTIR) spectrometry and scanning electron microscopy. The results showed a gradual change in the solid state properties of TA and a complete transformation into its amorphous form in 1: 8, 1: 4, 1: 2 and 1: 1 ratios at pH 3, 4, 5 and 6, respectively. FTIR spectrometry reveals the formation of a yellow polymorphic form of TA. Polymer molecular weight has also been observed to affect the drug transformation and interaction as the low molecular weight PA (M-w similar to 1800) was found to be most effective followed by its medium (M-v similar to 450 000) and high molecular weight (M-v similar to 3 000 000) forms. No signs of recrystallization in the TA-PA films were noted during the 12-week storage period. PA of low molecular weight has also been found more effective in inhibiting the recrystallization of the melt upon cooling thus proving a valuable polymer in producing stable amorphous solid dispersions of TA.
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