Investigation of the API distribution homogeneity in lyophilized product-pemetrexed disodium for injection by confocal micro-Raman spectroscopy mapping / 药学学报

ABSTRACT

The method of homogeneity evaluation for active pharmaceutical ingredient (API) spatial distribution in lyophilized product was investigated for the first time with confocal micro-Raman spectroscopy mapping, using pemetrexed disodium for injection as a model drug. Certain areas of the lyophilized product were scanned to obtain Raman spectra. The classical method ("peak clipping" method) was employed for mapping with characteristic Raman peaks of the API and the excipient. Due to the API being finely dispersed in the excipient in lyophilized products, the classical method cannot discriminate between the two ingredients making the distribution homogeneity difficult to evaluate. The "ratio of characteristic peak intensities" method was then utilized. Using this method, the relative intensity of the characteristic Raman peaks of the API to the excipient was applied for mapping and the relative content of API to excipient was calculated for a homogeneity evaluation of the drug distribution. The validation of this method showed a good linear relationship between the relative intensity and the relative content of API to excipient (r2 > 0.99), and the precision and recovery were adequate for homogeneity evaluation of API by Raman spectroscopy mapping. Five products of pemetrexed disodium for injection from different manufacturers were tested through Raman maps applying this method and the histograms of relative Raman intensity were also plotted by frequency to help the homogeneity evaluation of drug distribution. The results showed that there were obvious differences in the drug distribution homogeneity from different products, where a more homogeneous API distribution was found in the brand product. This research provides a reliable method for the homogeneity evaluation of API distribution, which facilitates quality evaluation and process optimization of lyophilized products.