Quantification of Monomer Units in Insoluble Polymeric Active Pharmaceutical Ingredients Using Solid-State NMR...

Although extensive precautions are taken to limit batch-to-batch variation in pharmaceutical manufacturing, differences between lots may still exist, particularly in complex formulations. When polymerization is used in the production process, the potential for varying chain lengths and incorporation of different monomers increases the likelihood of batch-to-batch variation. This poses a significant challenge for demonstrating active pharmaceutical ingredient (API) sameness between the innovator and generic drug under development. Therefore, the ability to accurately analyze and quantify the relative amounts of active ingredients present in a formulated product is critically important. Solid-state nuclear magnetic resonance (SSNMR) spectroscopy was used to identify, quantify, and compare the relative amounts of the three polymer groups in the amorphous block copolymer drug, patiromer (Veltassa^®). Techniques such as cross polarization (CP) and magic angle spinning were used to quantify each polymer group while the importance of understanding CP dynamics to obtain quantitative data was also addressed. It was found that the magnetization transfer rate and chemical shift anisotropy for different functional groups present in patiromer play a large role when optimizing parameters for spectral acquisition. Once accounted for, the average patiromer lot contained 90.9%, 7.6%, and 1.5% carboxylate, aromatic, and aliphatic blocks, respectively, with little lot-to-lot variation between different dosage strengths and expiration dates. SSNMR proved to be a sensitive analytical technique for evaluating and quantifying different monomer groups present in patiromer. This procedure may serve as a guide for similar quantitation studies on complex drug products and for demonstrating API sameness during generic drug development.