Raman spectroscopy for the in-line polymer–drug quantification and solid state characterization during a pharmaceutical hot-melt extrusion process

The aim of this study was to evaluate the suitability of Raman spectroscopy as a Process Analytical Technology (PAT) tool for the in-line determination of the active pharmaceutical ingredient (API) concentration and the polymer–drug solid state during a pharmaceutical hot-melt extrusion process.For in-line API quantification, different metoprolol tartrate (MPT) – Eudragit® RL PO mixtures, containing 10%, 20%, 30% and 40% MPT, respectively, were extruded and monitored in-line in the die using Raman spectroscopy. A PLS model, regressing the MPT concentrations versus the in-line collected Raman spectra, was developed and validated, allowing real-time API concentration determination. The correlation between the predicted and real MPT concentrations of the validation samples is acceptable (R2 = 0.997). The predictive performance of the calibration model is rated by the root mean square error of prediction (RMSEP), which is 0.59%.Two different polymer–drug mixtures were prepared to evaluate the suitability of Raman spectroscopy for in-line polymer–drug solid state characterization. Mixture 1 contained 90% Eudragit® RS PO and 10% MPT and was extruded at 140 °C, hence producing a solid solution. Mixture 2 contained 60% Eudragit® RS PO and 40% MPT and was extruded at 105 °C, producing a solid dispersion. The Raman spectra collected during these extrusion processes provided two main observations. First, the MPT Raman peaks in the solid solution broadened compared to the corresponding solid dispersion peaks, indicating the presence of amorphous MPT. Second, peak shifts appeared in the spectra of the solid dispersion and solid solution compared to the physical mixtures, suggesting interactions between Eudragit® RS PO and MPT, most likely hydrogen bonds. These shifts were larger in the spectra of the solid solution. DSC analysis confirmed these Raman solid state observations and the interactions seen in the spectra. Raman spectroscopy is a potential PAT-tool for in-line determination of the API concentration and the polymer–drug solid state during pharmaceutical hot-melt extrusion.

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