Finding the Needle in the Haystack: Characterization of Trace Crystallinity in a Commercial Formulation of Paclitaxel Protein-Bound Particles by Raman Spectroscopy Enabled by Second Harmonic Generation Microscopy

Abstract

Second harmonic generation (SHG) microscopy was used to rapidly identify regions of interest for localized confocal Raman spectroscopy measurements in order to quantify crystallinity within lyophilized Abraxane powder (protein bound paclitaxel for injectable suspension). Water insoluble noncentrosymmetric crystalline particles ranging from ∼1 to 120 μm were identified by SHG, with wide variability in crystal size and frequency observed between several batches of Abraxane. By targeting the Raman analysis to these localized regions identified by SHG, the required measurement time was decreased over 2 orders of magnitude, from 8 h to 2 s. Experimental Raman spectra of SHG active domains in Abraxane were in good agreement with experimental spectra of pure crystalline paclitaxel. These collective results are consistent with up to 30% of the active ingredient being present as poorly soluble crystalline particulates in some batches of Abraxane.

Pharmaceutical solvates, hydrates and amorphous forms: A special emphasis on cocrystals

“…FTIR and Raman are the basis of chemical imaging, which makes them more important for pharmaceutical formulations as they can locate and differentiate different solid forms in the formulation [189][190][191]. Process induced changes like polymorphic transformation, dehydration or desolvation can be easily analyzed using chemical imaging techniques [192].…”

Calibration-Free Second Harmonic Generation (SHG) Image Analysis for Quantification of Trace Crystallinity Within Final Dosage Forms of Amorphous Solid Dispersions

“…In one recent departure from the signal integration approach for quantification, Schmitt et al directly recovered the particle size distribution via image analysis for poorly soluble particulates present in commercially available formulations of Abraxane . 22 Second harmonic generation-active particles as large as 120 mm in diameter were observed within the commercial lyophilized powders. In comparison to signal integration, this particle counting approach has the potential to further lower the limits of detection by SHG (by analogy with photon counting).…”

“…Crystals of homochiral molecules generally fall into space groups that are symmetry-allowed for SHG, providing highly selective and sensitive detection of homochiral crystalline APIs. [22][23][24][25][26][27][28] Limits of detection for chiral crystallinity using SHG have been reported in the parts per trillion (ppt) regime in melt-quenched films and in the parts per million (ppm) regime for powders. 23,29 More recently, SHG has been used to monitor changes in crystallinity in amorphous solid dispersions in spray-dried dispersions.…”

“…Nonlinear optical (NLO) imaging has proven to be a successful method in the pharmaceutical field for the sensitive detection of trace crystallization in amorphous systems. 22,23 Second harmonic generation (SHG) is a coherent process, in which the incoming light is converted to light of twice the frequency. The particular symmetry properties of SHG only permit this second-order process in ordered non-centrosymmetric systems; amorphous or disordered systems do not generate coherent SHG.…”

Elucidation of Compression-Induced Surface Crystallization in Amorphous Tablets Using Sum Frequency Generation (SFG) Microscopy

“…The use of SHG has been combined with a microscope to image the distribution of crystallinity in amorphous materials (25)(26)(27)(28)(29)(30)(31). Wanapun et al investigated the distribution and kinetics of crystallization of amorphous griseofulvin and chlorpromamide at temperatures above the drugs' respective glass transitions using SHG imaging and compared the onset of crystallizations with those obtained using polarized light microscope (PLM) (29).…”