Evaluation of an in-line NIR spectroscopic method for the determination of the residence time in a tablet press.

In the current study, the ability to use in-line NIR inside the feed frame of a tablet press to monitor the residence time distribution inside the tablet press was investigated. Pulse-response experiments were performed. In-line measurements inside the feed frame were compared to measurements on the actual produced tablets and the influence of different tableting parameters on the concentration profiles were studied. Turret speed had a major influence on the concentration profiles and RTD parameters. The in-line and off-line concentration profiles did not align with each other as spiking material was still detected in the tablets when no spiking material was observed in the powder blend by the in-line measuring method. The cause of this mismatch between the in-line and off-line curves was the in-line measuring position. By adjusting the position of the NIR probe to the bottom of the feed frame instead of at the top of the feed frame, a perfect alignment between in-line and off-line concentration curves was acquired. In-line measurements at the bottom of the feed frame could, if optimisation to avoid probe fouling is possible, be ideal for real-time measurement and control of the blend concentration during tableting. When probe fouling cannot be avoided, the correlation between the in-line measured concentration at the top of the feed frame and the concentration of the produced tablets should be investigated and modelled to enable real-time measurement and control based on in-line measurements.

Measurement of residence time distributions and material tracking on three continuous manufacturing lines.

Over the recent decade, benefits of continuous manufacturing (CM) of pharmaceutical products have been acknowledged widely. In contrast to batch processes, the product is not physically separated into batches in CM, which creates a few challenges. Product release is done for batches that should have a uniform quality over time, materials need to be tracked along the line, and locations to reject product must be established. To enable these, the residence time distributions (RTDs) of all unit operations must be known. In this paper, three CM tableting lines, each employing a different granulation technique, were investigated. The RTDs of their main unit operations were characterized, utilizing different measurement techniques successfully. All of these RTD measurement techniques could have been performed in any of the lines. The differences were related to the techniques themselves. Overall, external tracer with in-line Near-Infrared detection or color tracer with video recording proved most usable techniques, with few limitations. The RTDs for full lines were calculated by convoluting the unit operation RTDs, which enables material tracking through entire lines. The lines exhibited both truly continuous and quasi-continuous unit operations. Quasi-continuous unit operations divide the material stream into lots that can be utilized for tracking and rejection.

Modeling of Semicontinuous Fluid Bed Drying of Pharmaceutical Granules With Respect to Granule Size.

In the transition of the pharmaceutical industry from batchwise to continuous drug product manufacturing, the drying process has proven challenging to control and understand. In a semicontinuous fluid bed dryer, part of the ConsiGma™ wet granulation line, the aforementioned production methods converge. Previous research has shown that the evolution of moisture content of the material in this system shows strong variation in function of the granule size, making the accurate prediction of this pharmaceutical critical quality attribute a complex case. In this work, the evolution of moisture content of the material in the system is modeled by a bottom-up approach. A single granule drying kinetics model is used to predict the moisture content evolution of a batch of material of a heterogeneous particle size, where it is the first time that the single granule drying mechanism is validated for different granule sizes. The batch approach was validated when the continuous material inflow rate and filling time of the dryer cell are constant. The original single granule drying kinetics model has been extended to capture the granules' equilibrium moisture content. Finally, the influence of drying air temperature is captured well with a droplet energy balance for the granules.

Development and validation of an in-line NIR spectroscopic method for continuous blend potency determination in the feed frame of a tablet press.

A calibration model for in-line API quantification based on near infrared (NIR) spectra collection during tableting in the tablet press feed frame was developed and validated. First, the measurement set-up was optimised and the effect of filling degree of the feed frame on the NIR spectra was investigated. Secondly, a predictive API quantification model was developed and validated by calculating the accuracy profile based on the analysis results of validation experiments. Furthermore, based on the data of the accuracy profile, the measurement uncertainty was determined. Finally, the robustness of the API quantification model was evaluated. An NIR probe (SentroPAT FO) was implemented into the feed frame of a rotary tablet press (Modul™ P) to monitor physical mixtures of a model API (sodium saccharine) and excipients with two different API target concentrations: 5 and 20% (w/w). Cutting notches into the paddle wheel fingers did avoid disturbances of the NIR signal caused by the rotating paddle wheel fingers and hence allowed better and more complete feed frame monitoring. The effect of the design of the notched paddle wheel fingers was also investigated and elucidated that straight paddle wheel fingers did cause less variation in NIR signal compared to curved paddle wheel fingers. The filling degree of the feed frame was reflected in the raw NIR spectra. Several different calibration models for the prediction of the API content were developed, based on the use of single spectra or averaged spectra, and using partial least squares (PLS) regression or ratio models. These predictive models were then evaluated and validated by processing physical mixtures with different API concentrations not used in the calibration models (validation set). The ß-expectation tolerance intervals were calculated for each model and for each of the validated API concentration levels (ß was set at 95%). PLS models showed the best predictive performance. For each examined saccharine concentration range (i.e., between 4.5 and 6.5% and between 15 and 25%), at least 95% of future measurements will not deviate more than 15% from the true value.

Blend uniformity evaluation during continuous mixing in a twin screw granulator by in-line NIR using a moving F-test.

This study focuses on the twin screw granulator of a continuous from-powder-to-tablet production line. Whereas powder dosing into the granulation unit is possible from a container of preblended material, a truly continuous process uses several feeders (each one dosing an individual ingredient) and relies on a continuous blending step prior to granulation. The aim of the current study was to investigate the in-line blending capacity of this twin screw granulator, equipped with conveying elements only. The feasibility of in-line NIR (SentroPAT, Sentronic GmbH, Dresden, Germany) spectroscopy for evaluating the blend uniformity of powders after the granulator was tested. Anhydrous theophylline was used as a tracer molecule and was blended with lactose monohydrate. Theophylline and lactose were both fed from a different feeder into the twin screw granulator barrel. Both homogeneous mixtures and mixing experiments with induced errors were investigated. The in-line spectroscopic analyses showed that the twin screw granulator is a useful tool for in-line blending in different conditions. The blend homogeneity was evaluated by means of a novel statistical method being the moving F-test method in which the variance between two blocks of collected NIR spectra is evaluated. The α- and ß-error of the moving F-test are controlled by using the appropriate block size of spectra. The moving F-test method showed to be an appropriate calibration and maintenance free method for blend homogeneity evaluation during continuous mixing.

Linking granulation performance with residence time and granulation liquid distributions in twin-screw granulation: An experimental investigation.

Twin-screw granulation is a promising wet granulation technique for the continuous manufacturing of pharmaceutical solid dosage forms. A twin screw granulator displays a short residence time. Thus, the solid-liquid mixing must be achieved quickly by appropriate arrangement of transport and kneading elements in the granulator screw allowing the production of granules with a size distribution appropriate for tableting. The distribution of residence time and granulation liquid is governed by the field conditions (such as location and length of mixing zones) in the twin-screw granulator, thus contain interesting information on granulation time, mixing and resulting sub-processes such as wetting, aggregation and breakage. In this study, the impact of process (feed rate, screw speed and liquid-to-solid ratio) and equipment parameters (number of kneading discs and stagger angle) on the residence time (distribution), the granulation liquid-powder mixing and the resulting granule size distributions during twin-screw granulation were investigated. Residence time and axial mixing data was extracted from tracer maps and the solid-liquid mixing was quantified from moisture maps, obtained by monitoring the granules at the granulator outlet using near infra-red chemical imaging (NIR-CI). The granule size distribution was measured using the sieving method. An increasing screw speed dominantly reduced the mean residence time. Interaction of material throughput with the screw speed and with the number of kneading discs led to most variation in the studied responses including residence time and mixing capacity. At a high screw speed, granulation yield improved due to high axial mixing. However, increasing material throughput quickly lowers the yield due to insufficient mixing of liquid and powder. Moreover, increasing liquid-to-solid ratio resulted in more oversized granules, and the fraction of oversized granules further increased at higher throughput. Although an increasing number of kneading discs was found to be critical for achieving a uniform distribution of the granulation liquid, the granulation performance was hampered due to insufficient solid-liquid mixing capacity of the current kneading discs which is essential for wet granulation. Thus, a balance between material throughput and screw speed should be strived for in order to achieve a specific granulation time and solid-liquid mixing for high granulation yield. Additionally, more efforts are needed both in modification of the screw configuration as well as the geometry of the mixing elements to improve the mixing capacity of the twin-screw granulator. The results from the current experimental study improved the understanding regarding the interplay between granulation time and the axial and solid-liquid mixing responsible for the granulation performance in twin-screw wet granulation.