(T1230-11-63) Laser Directed Infrared (LDIR) Imaging to Track the Evolution of Polymorphic Transformation During Stability Studies on Ritonavir Tablets

Purpose: Vibrational spectroscopic imaging techniques such as Raman mapping or Near Infrared (NIR) imaging can identify active pharmaceutical ingredient (API) and excipients in high resolution images of pharmaceutical products. Nevertheless, Raman mapping or NIR imaging are limited in their ability to track the evolution of any physical or chemical processes of API/excipient in real-time due to lengthy data collection times, especially over large areas. A new vibrational imaging technique, Laser directed infrared spectroscopy (LDIR) imaging, uses a tunable quantum cascade laser (QCL) making it possible to reduce data collection time to minutes or seconds for entire pharmaceutical tablet surfaces without losing critical physicochemical information such as chemical identity, particle size and shape, and distribution of components which make it capable to track any physical or chemical processes of API/excipients on the surface. Furthermore, LDIR imaging can differentiate between polymorphic forms.

Methods: Ritonavir, a well-known polymorphic API, was tested here to understand real-time evolution between amorphous, form I and form II at 40 ℃ and 75% relative humidity with LDIR imaging as a follow-up study (Anal. Chem. 2023, 95, 41, 15325–15332) to understand observation of polymorphism in real world samples. The role of spiking dosage of impurities (either Form I or Form II) and origin of amorphous ritonavir were tested. Amorphous ritonavir was prepared from Form I and Form II separately by solvent evaporation method. Formulations with 0.0, 0.2, 2.0, and 20% impurities were prepared with amorphous ritonavir and co-povidone polymer prior to tablet preparation with a manual tablet press. A modified classification LDIR imaging method, developed for four components (co-povidone polymer, ritonavir amorphous, Form I, and Form II), was used to collect data for an area of 2 mm x 2 mm with a step-size of 5 µm in 2 min on in-house prepared tablets. Hence, LDIR imaging allowed for tracking the evolution of API in the tablet surface with samples only needing to be removed from the stability chamber for less than 5 min. Analysis was performed on the LDIR images to extract number of domains (particles), particle size as feret diameter and percent area coverage of components.

Results: X-ray powder diffraction (XRPD) showed the purity of prepared amorphous ritonavir. A modified classification LDIR imaging method developed for Co-povidone polymer, ritonavir amorphous, form I, and form II with the peak/baseline wavenumber of 1729/1751, 1489/1518, 1712/1635, and 1700/1619 cm^-1, respectively. In control experiments, it was observed that co-povidone polymer/Form I/Form II were stable inside stability chamber for 7 days, however, co-povidone polymer was found to swell at 75% humidity. The kinetic crystallization of amorphous ritonavir in tablet form is shown in Figure 1. LDIR images showed the transformation (Figure 1A) of amorphous ritonavir with storage time inside stability chamber. It was observed that amorphous ritonavir was crystallize into Form I at that condition and kinetic plots for both components are presented in Figure 1B. Individual particles were found to aggregate at the stressed condition (see Figure 1C). Figure 1 showed faster aggregation initially followed by prompt crystallization at the later time like the Flory-Huggin model. Spiking dose of Form I is inversely related with the disappearance of amorphous ritonavir shown in Table 1. Amorphous ritonavir was found to crystallize to Form I only regardless of the origin of amorphous ritonavir. However, amorphous ritonavir prepared from Form II needed longer time (~78h) to disappear in compared to the amorphous ritonavir prepared from Form I (~32h) in Table 1.

Conclusion: Amorphous ritonavir was found to aggregate and crystallize into form I only at the experimental condition regardless of the origin of amorphous ritonavir (form I or II). Both (aggregation and crystallization) processes proceeded in accordance with Flory-Huggin model. Spiking dosage of impurities were found to promote faster crystallization of amorphous ritonavir into Form I. LDIR imaging has the potential to rapidly track polymorphic conversions over time within tablets which could be a valuable at-line PAT tool to understand and mitigate this process.

Acknowledgements: This project was supported in part by an appointment to the Research Participation Program at the U.S. Food and Drug Administration administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and the U.S. Food and Drug Administration.
Disclaimer: The findings and conclusions in this presentation reflects the views of the author and should not be construed to represent FDA’s views or policies.


Figure 1. Tracking the crystallization of amorphous ritonavir to Form I inside stability chamber at 40 ℃ and 75% relative humidity. Top) LDIR images of the tablet surface with storage times, A) Evolution of % area coverages for components shown in LDIR images, and B) Particle size evolution of specific particles denoted in LDIR images.


Table 1. Testing the role of spiking dosage and origin of amorphous ritonavir at stressed conditions (40 ℃ and 75% relative humidity)