Understanding die fill variation during mini-tablet production

The revival of the mini-tablets: Recent advancements, classifications and expectations for the future

Mini-tablets have recently raised huge interest in pharmaceutical industry. The present review aims to identify the rational, the opportunities and challenges of this emerging small solid drug dosage form by a structured literature review following the PRISMA algorithm. In total, more than 5,000 literature and patent sources have been found starting with the very first in the 60s of the past century, followed by the first multiparticular products using mini-tablets with pancreatin (Panzytrat® by the former BASF subsidiary Knoll/Nordmark) authorized in 1985. There seems to be a second boost of common interest in the 2000s when clinical studies demonstrated that one or more mini-tablets could enable superior drug administration even in very young patients including neonates over the former gold standard, a liquid drug preparation. Several pharmaceutical companies immediately started clinical development programs using the mini-tablet concept and the first products have been recently authorized by the competent authorities. Superiority was given as the mini-tablets ease the swallowing procedure compared to conventional tablets, enable various modified drug release opportunities including taste-masking by film-coating technology and provide excellent drug stability compared to liquid oral dosage forms. Due to these product attributes they are particularly beneficial to children and their caregivers. Furthermore, there is potential for precise individual drug dosing by counting adequate amounts of the multiple drug carriers. Most recently, two novel products with different concepts were authorized by the EMA and entered the market which are highlighted in this review: the first orodispersible mini-tablet with enalapril maleate for congenital heart failure (Aqumeldi® from Proveca Pharma) and the first single unit mini-tablet with matrix-type controlled melatonin release for insomnia (Slenyto® from Neurim Pharmaceuticals). Our review reveals, that the majority of the published scientific papers use co-processed, ready-to-use excipients for the orodispersible mini-tablet formulations. However, traditional fillers such as microcrystalline cellulose or lactose have also been used for immediate release mini-tablets after adding a (super)disintegrant and a lubricant. The manufacturing of mini-tablets is conducted on conventional rotary tablet presses, predominantly equipped with multi-tip toolings to improve the yield or production speed. Scaling-up has been successfully realized from compaction simulators to pilot and production scale. Film-coatings enabling gastric resistance, taste masking or sustained-release properties have been realized in both fluid-bed and drum coaters using the same polymers as for conventional tablets. There is still a significant lack in regulatory guidance despite the recent success of the mini-tablet concept, starting from suitable characterization methods in the pharmacopoeias up to the design and conduct of clinical studies on mini-tablets.

The effect of material properties and process parameters on die filling using double-tip tooling: A PLS-model-based analysis

Up-scaling on a rotary tablet press by increasing turret speed can have a negative effect on die filling performance, as the dies have less time to be filled, leading to high tablet weight variability. For this reason, double-tip tooling is investigated, where a punch contains 2 tips instead of 1, doubling the throughput without the need to increase turret speed. However, when using multi-tip punches, one has to bear in mind that punch responses, e.g. pre- and main compression force, are the sum of each tip. When using these responses to assess tablet properties during compression, it is assumed that they can be divided over the total number of punch tips, i.e. an equal contribution of each tip to the response. This assumption can only hold when die filling is uniform across all tips. In this work, the impact of formulation material properties and process settings (X) upon die filling performance for double-tip tooling (Y) was studied, by developing and analyzing a PLS model regressing X versus Y. Additionally, this model enables the estimation of die filling variability based on material characterization data, eliminating the need for extensive tableting experiments and reducing material consumption in R&D.

Using in-line measurement and statistical analyses to predict tablet properties compressed using a Styl'One compaction simulator: A high shear wet granulation study

High shear wet granulation (HSWG) is widely used in tablet manufacturing mainly because of its advantages in improving flowability, powder handling, process run time, size distribution, and preventing segregation. In-line process analytical technology measurements are essential in capturing detailed particle dynamics and presenting real-time data to uncover the complexity of the HSWG process and ultimately for process control. This study is to find relationships between Lenterra in-line measurements and granule properties and tablet properties. The Styl'One Evolution compaction simulator was used to produce tablets that mimic an industrial rotary tablet press, which is different from the Gamlen used in our previous study. Furthermore, this research provided an understanding of the granule growth mechanisms during the granulation process, revealing that an induction granule growth mechanism occurs. This is specific to the material and process conditions studied. The model developed using data from a Gamlen tabletting press demonstrated high predictability for data generated using the Styl'One Evolution compaction simulator, with an R2 value of 0.9535 and a RMSE of 0.4040 MPa. This finding highlights the ability of the model to predict tablet tensile strength independently of the compaction machine used, suggesting industrial-scale applications. The findings of this research provide substantial advances in understanding and monitoring the granulation process, with promising implications for scalable industrial processes.

Effects of Shape on the Disintegration Time and Friability of Sucroferric Oxyhydroxide-Containing Mini-Tablets

Sucroferric oxyhydroxide is a phosphate binder for the treatment of hyperphosphatemia in patients with chronic kidney disease undergoing dialysis. This study aimed to determine the effects of tablet size, shape, and tensile strength on disintegration time and friability of sucroferric oxyhydroxide-containing mini-tablets. A linear relationship between the disintegration time and tensile strength was observed across all mini-tablets, except for those with smaller tablets (diameters: <1.8 mm). However, the relationship between friability and tensile strength was not significantly correlated under linear or exponential approximations. Explaining friability solely based on tensile strength was challenging, indicating the role of tablet shape. To visualize the effects of mini-tablet shapes and tensile strength on their disintegration time and friability, response aspects were analyzed. The response surface analysis revealed that the disintegration time was not affected by the tablet shape. The friability of the mini-tablets with a cup depth/diameter of 0.209 was lower (<0.2) than that of tablets with other cup depth/diameter across all tested ranges of tensile strength (1-6). A cup depth/diameter of 0.2 was identified as optimal for minimizing the friability of mini-tablets and can be implemented in commercial production without issues. In conclusion, tablet shape should be carefully considered during the development of mini-tablets to ensure low friability.

Challenges encountered in the transfer of atorvastatin tablet manufacturing - commercial batch-based production as a basis for small-scale continuous tablet manufacturing tests

As is the case with batch-based tableting processes, continuous tablet manufacturing can be conducted by direct compression or with a granulation step such as dry or wet granulation included in the production procedure. In this work, continuous manufacturing tests were performed with a commercial tablet formulation, while maintaining its original material composition. Challenges were encountered with the feeding performance of the API during initial tests which required designing different powder pre-blend compositions. After the pre-blend optimization phase, granules were prepared with a roller compactor. Tableting was conducted with the granules and an additional brief continuous direct compression run was completed with some ungranulated mixture. The tablets were assessed with off-line tests, applying the quality requirements demanded for the batch-manufactured product. Chemical maps were obtained by Raman mapping and elemental maps by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Large variations in both tablet weights and breaking forces were observed in all tested samples, resulting in significant quality complications. It was suspected that the API tended to adhere to the process equipment, accounting for the low API content in the powder mixture and tablets. These results suggest that this API or the tablet composition was unsuitable for manufacturing in a continuous line; further testing could be continued with different materials and changes in the process.

Dose Titration of Solid Dosage Forms via FDM 3D-Printed Mini-Tablets

The robustness of 3D-printed mini-tablets as a platform to administer milligram dosages, intended for age-specific therapy, without the need of tablet splitting while maintaining similar release profiles, was investigated. Griseofulvin, as a model poorly water-soluble drug, and hydroxypropyl cellulose along with Kollicoat Protect as polymers were used to prepare filaments at 1-20% drug concentrations via hot-melt extrusion (HME). Higher drug concentrations served for testing the feasibility of a reduced number of mini-tablets to be administered. A reliable dose titration in the range 0.19-3.91 mg at a high accuracy (R2 of 0.999) was achieved through composite unit (multi-unit) mini-tablets. All mini-tablets produced had excellent content uniformity and their label claim values were within the acceptable range, proving that HME processing followed by 3D printing promotes content uniformity even for mini-tablets containing low drug doses (0.19 mg). Remarkably, the proposed approach allowed achieving similar drug release profiles via composite unit mini-tablets as well as single mini-tablets at high drug concentrations. In contrast, split tablets demonstrated different release behaviors, attributed to their size and shape differences. Overall, the distinct advantages of mini-tablets to provide dose flexibility while maintaining similar release profiles was demonstrated.

Implementing the Design of Experiments (DoE) Concept into the Development Phase of Orodispersible Minitablets (ODMTs) Containing Melatonin

Development of orodispersible minitablets (ODMTs) requires consideration of aspects related to small dimensions, while ensuring short disintegration time with sufficient mechanical stability. In order to meet these and other critical quality attributes (CQAs), quality by design is encouraged. According to this approach, formulation and compression process factors were systematically studied using design of experiments (Plackett-Burman for screening purposes, full and fractional factorial design for in-depth characterization) to understand their influence on CQAs of orodispersible minitablets containing melatonin. Mathematical models describing the relationships between processing variables and attributes such as resistance to crushing and disintegration time were successfully developed, characterized by high coefficients of determination (R²_adj = 0.90-0.97) and prediction errors in the range (+2.4 to -10.8%). In conclusion, based on these models, the design space was created for melatonin ODMTs, ensuring the product's quality and process robustness. Moreover, the study demonstrated the suitability of texture analysis as an alternative to compendial measurement methods of resistance to crushing and disintegration time. Graphical abstract.

Effects of Manufacturing Process Variables on the Tablet Weight Variation of Mini-tablets Clarified by a Definitive Screening Design

This study investigated the effect of manufacturing process variables of mini-tablets, in particular, the effect of process variables concerning fluidized bed granulation on tablet weight variation. Test granules were produced with different granulation conditions according to a definitive screening design (DSD). The five evaluated factors assigned to DSD were: the grinding speed of the sample mill at the grinding process of the active pharmaceutical ingredient (X1), microcrystalline cellulose content in granules (X2), inlet air temperature (X3), binder concentration (X4) and the spray speed of the binder solution (X5) at the granulation process. First, the relationships between the evaluated factors and the granule properties were investigated. As a result of the DSD analysis, the mode of action of granulation parameters on the granule properties was fully characterized. Subsequently, the variation in tablet weight was examined. In addition to mini-tablets (3 mm diameter), this experiment assessed regular tablets (8 mm diameter). From the results for regular tablets, the variation in tablet weight was affected by the flowability of granules. By contrast, regarding the mini-tablets, no significant effect on the variation of tablet weight was found from the evaluated factors. From this result, this study further focused on other important factors besides the granulation process, and then the effect of the die-hole position of the multiple-tip tooling on tablet weight variation was proven to be significant. Our findings provide a better understanding of manufacturing mini-tablets.

Transfer and scale-up of the manufacturing of orodispersible mini-tablets from a compaction simulator to an industrial rotary tablet press

Orodispersible mini-tablets (ODMTs) are a promising dosage form for the pediatric use showing increasing interest from pharmaceutical industry. However, a scale-up process for ODMTs from a compaction simulator to a rotary tablet press following FDA and EMA guidelines has not been performed and investigated yet. Isomalt (galenIQ™721) and Ludiflash® both excipients with proven suitability for the development of ODMTs have been investigated in transfer and scale-up from a compaction simulator to a rotary tablet press. ODMTs with isomalt and Ludiflash® were produced on the rotary tablet press monitoring the product temperature over time and assessing the properties of the residual powder in the feed shoe. Critical quality attributes like tensile strength, mass and disintegration time were evaluated. The transfer from compaction simulator to rotary tablet press succeeded as for both excipients similar disintegration times, tabletability and compactibility profiles were obtained. However, during scale-up, disintegration time significantly increases over time for both excipients. Monitoring of the product temperature revealed that with increasing batch size the product temperature increases as well having a significant impact on disintegration time. The properties of ODMTs produced with the residual powder are comparable in tabletability and disintegration time compared with ODMTs produced from fresh powder.

Effect of colloidal silicon dioxide and moisture on powder flow properties: Predicting in-process performance using image-based analysis

The effect of colloidal silicon dioxide (CSD) on powder flow properties of poor-flowing excipient lactose 200 M was investigated. Binary mixtures of different ratios of CSD as glidant were examined using a modern image-based flow measuring technique. Special attention was placed to subtle variations in powder flow from small changes in glidant concentration (0.025% w/w). Understanding the modes of interaction of particles and their effects on flowability using the method predicted the die filling performance during tablet manufacture. In addition, the importance of moisture content on powder flow properties was empirically underlined. A more efficient range of CSD was detected from 0.10 to 0.50% w/w in most of the tested conditions, which revealed a significant improvement in powder flow performance compared to higher amounts typically handled in the pharmaceutical industry.

Evaluation of Weight Variation in Mini-Tablets Manufactured by a Multiple-Tip Tool

Recently, owing to their pharmaceutical and clinical utility, mini-tablets have been well studied by researchers. Mini-tablets are usually manufactured by compression molding using a multiple-tip tool in a rotary tableting machine. Owing to their special structure, ensuring uniformity is a very important challenge in the manufacturability of mini-tablets using the multiple-tip tool. In this study, we aimed to evaluate the weight variation in mini-tablets produced by a multiple-tip tool, which is considered to be the root cause affecting the uniformity, and to investigate the physical properties of drug granules and tableting conditions in a rotary tableting machine that could reduce this weight variation. In addition, the relationship between these factors and response was visualized using response surface analysis. It was shown that the weight variation in mini-tablets produced by a multiple-tip tool was reduced when using a forced feeder compared with an open feeder. Furthermore, in the case of an open feeder, the optimal range of the average particle size diameter of drug granules and the rotational speed of the rotating disc in the rotary tableting machine were determined from response surface analysis. It was suggested that it is possible to reduce the weight variation in the mini-tablets by selecting drug granules with an average particle size diameter of 100-150 µm and using tableting conditions with a rotational speed of 40-60 rpm. This study elucidated the factors that affect uniformity and determined their optimal range for the manufacture of mini-tablets.

The Development of Minitablets for a Pediatric Dosage Form for a Combination Therapy

Minitablets are an appealing option for an age-appropriate pediatric dosage form. In particular, for combination therapies where multiple active ingredients are dosed simultaneously, the use of minitablets will enable independent adjustments of each dose. The work presented describes the development of Compound A and Compound B minitablets for a combination therapy. Since both actives are formulated as spray dried amorphous solid dispersions (ASDs) due to low solubility of their crystalline forms, the choice of minitablets for the pediatric dosage form allows the application of the same formulation strategy across different age groups. To address the potential need for taste-masking, an ethylcellulose-hydroxypropyl cellulose coating system was developed. In-vitro performance testing was conducted to guide coating development and to ensure proper taste-masking without slowing down API dissolution in the GI tract that can negatively impact exposures. As a result, the exposure of orally dosed coated tablets was comparable to those of uncoated minitablets in the canine model. The work presented can serve as a case study on how minitablets can be designed and developed as an appropriate pediatric dosage form for a combination therapy comprised of ASD of active ingredients.

Investigation on the impact of powder arching in small die filling

The flow of particulate materials is critical during processes such as mixing, compression and packing. Non-cohesive arching, a feature characteristic of coarse and free-flowing particles, has been studied extensively for silos and hoppers. However, the arching of powders during die fill has received much less attention. In this study, die fill performance of coarse and free-flowing nonpareils was evaluated using a specially designed die filling device in order to investigate the impact of non-cohesive arching during die fill under gravity flow. Through evaluating die fill performance, the arching phenomenon during dynamic conditions of die fill could be captured. Nonpareils with large particle size increased the likelihood of arching and caused poorer die fill performance for narrow orifices. In contrast, die fill in large orifices was generally better with larger particles due to reduced inter-particulate friction. Both particle size and size distribution influenced non-cohesive arching during die fill. Forced feeding did not appear to affect die fill performance and non-cohesive arching. A critical particle size range beyond which die fill performance would decrease, particularly for the narrow orifices, was identified. Findings from this study provided a better insight into non-cohesive arching during die fill.

The Effects of Feed Frame Parameters and Turret Speed on Mini-Tablet Compression

Die filling is a critical process step during tablet production as it defines the tablet weight. Achieving die fill consistency during production of mini-tablets, tablets with diameters ≤6 mm, is considerably more challenging. Although die filling in rotary presses had been studied in relation to the feed paddle design, paddle speed, and turret speed, it is unclear how these process variables could impact mini-tablet production and product properties. In this study, 1.8 and 3 mm mini-tablets were prepared using a rotary press with multiple-tip tooling using different process configurations. Mini-tablet weight variation within and across compaction cycles were determined using data from compression roller displacement and mini-tablet weight. Higher die fill densities were achieved with a flat feed wheel paddle and high paddle speed. This was attributed to better granule fluidization in the feed frame, which also increased the intercycle weight variation and reduced tensile strength. The turret speed did not impact mini-tablet properties significantly. Granule overlubrication in the feed frame potentially reduced mini-tablet tensile strength during compaction. The number of paddle passes in the die fill region was correlated to mini-tablet die fill performance. Findings from this study could provide better insights into the relationship between process variables and mini-tablet product quality.