Powder flow in an automated uniaxial tester and an annular shear cell: a study of pharmaceutical excipients and analytical data comparison

A step closer to continuous buffer preparation from solids: Predicting powder compaction and how to prevent it

The preparation of buffer solutions used in the biopharmaceutical industry is typically performed manually by the addition of one or multiple buffering reagents to water. Recently, the adaptation of powder feeders for continuous solid feeding was demonstrated for continuous buffer preparation. However, the intrinsic characteristics of powders can change the stability of the process, due to the hygroscopic nature of some substances and humidity induced caking and compaction behavior, but there is no simple and easy methodology available predicting this behavior for buffer species. To predict which buffering reagents are suitable without special precautions and investigate their behavior, force displacement measurements were conducted with a customized rheometer over 18hours. While most of the eight investigated buffering reagents indicated uniform compaction, especially sodium acetate and dipotassium hydrogen phosphate (K₂HPO₄) showed a significant increase in yield stress after 2hours. Experiments conducted with a 3D printed miniaturized screw conveyor confirmed the increased yield stress measurement by visible compaction and failure of the feeding. By taking additional precautions and adjusting the design of the hopper, we demonstrated a highly linear profile of all buffering reagents over a duration of 12 and 24hours. We showed that force displacement measurements accurately predict the behavior of buffer components in continuous feeding devices for continuous buffer preparation and are a valuable tool to identify buffer components that need special precautions. Stable, precise feeding of all tested buffer components was demonstrated, showing the importance of identifying buffers that need a specialized setup with a fast methodology.

Process Model Approach to Predict Tablet Weight Variability for Direct Compression Formulations at Pilot and Production Scale

Optimizing processing conditions to achieve a critical quality attribute (CQA) is an integral part of pharmaceutical quality by design (QbD). It identifies combinations of material and processing parameters ensuring that processing conditions achieve a targeted CQA. Optimum processing conditions are formulation and equipment-dependent. Therefore, it is challenging to translate a process design between formulations, pilot-scale and production-scale equipment. In this study, an empirical model was developed to determine optimum processing conditions for direct compression formulations with varying flow properties, across pilot- and production-scale tablet presses. The CQA of interest was tablet weight variability, expressed as percentage relative standard deviation. An experimental design was executed for three model placebo blends with varying flow properties. These blends were compacted on one pilot-scale and two production-scale presses. The process model developed enabled the optimization of processing parameters for each formulation, on each press, with respect to a target tablet weight variability of <1%RSD. The model developed was successfully validated using data for additional placebo and active formulations. Validation formulations were benchmarked to formulations used for model development, employing permeability index values to indicate blend flow.

Lactose monohydrate flow characterization using shear cell method

The flow properties of pharmaceutical powders have a great importance in the manufacturing of solid dosage forms. In order to ensure the performance in the production line this parameter must be determined. There are several methods described in European Pharmacopeia that are used to measure these properties. Some of them were used in this study and the results obtained from conventional methods (Conv) and shear cell using the powder flow tester (PFT) showed differences that were more evident in fractions with smaller particle size (F < 63) and for bulk powder (F_Total). The various powder behaviors showed to be related with the size of the particles. An increase of the ff_c (Flow Index) was observed with the increase of the particle size. It was also found for the different fractions that the ff_c always increases with increasing major principal consolidation stress (σ₁). This study shown to be predictive because it also allowed the behavior profiles of other LactMN fractions to be known by interpolation of the median size (Dv50) or σ₁ values ranged between the studied intervals. Furthermore, it was also observed that ff_c of the F_Total was similar to the F < 63, showing the same behavior under σ₁. The occurrence of caking was not observed.

Pharmaceutical excipients properties and screw feeder performance in continuous processing lines: a Quality by Design (QbD) approach

Screw feeder performance is a critical aspect in continuous manufacturing processes. Pharmaceutical excipients, such as mannitol, microcrystalline cellulose, lactose monohydrate, and anhydrous dibasic calcium phosphate can present problems in ensuring a continuous stable feed rate due to their sub-optimal flow properties. In alignment with Quality by Design (QbD) goals, the aim of this work was to identify and explain critical sources of variability of some powder excipients delivery by screw feeding, in particular to continuous processing lines. Pharmaceutical excipients with a wide range of material properties were selected, and the impact of their flow and density properties on screw feeder performance was investigated. The analysis of the powder conveying by the screws was performed at different hopper fills and different screw speeds. A multivariable model involving bulk density (CBD) and parameters from FT4 dynamic downwards testing (SI) and dynamic upwards testing (SE) explained 95.7% of excipients feed rates (p < .001). The study gathers valuable information about the screw feeder performance and input materials properties that can help process understanding and QbD-based development of solid dosage forms in continuous processing lines.