(T1330-02-10) Evaluating the Impact of an Ultra-High Solids Film Coating System on Process Times and Tablet Aesthetics

Purpose: Ultra-high solid film coating systems are designed to increase productivity while maintaining excellent product aesthetics and high gloss. State-of-the-art coating process equipment and these improved film coating systems facilitate shorter processing times due to more intense spray application and fast drying processes combined with the possibility to spray coating dispersions up to 35 % of solids. One specific challenge for high-solid coating systems is achieving good color uniformity within a batch (batch homogeneity) and between multiple batches (batch conformance). Furthermore, low surface roughness and high gloss of produced tablets are preferable aesthetic tablet characteristics. This study aimed to evaluate tablets coated with an optimized ultra-high solids film coating system in an L.B. Bohle TriPan drum coater in a wide range of processing parameters.

Methods: Round placebo tablets (220mg, 8mm) were used as the substrate for this study. The tablets were coated with HPMC-based Aquarius™ Prime Clear and HPC/copovidone-based ultra-high solids Aquarius™ Genesis yellow. All coating trials were conducted in a BFC 50 TriPan full perforated coating pan (L.B. Bohle, Ennigerloh, Germany) equipped with six spray nozzles (type 970, Schlick, Germany). The batch size was 20 kg. Coating weight uniformity analysis was conducted on 200 individually marked tracer tablets. The batch was coated with HPMC-based Clear, and the coating process was stopped at different weight gain steps (0.5%, 1.0%, 1.5%, 2.0%, 3.0%, 4.0%, 5.0%, 6.5%, 8.0%, and 10.0%) and consequently unloaded. The marked tablets were manually picked out, weighed, and returned to the batch, and the next coating trial segment was started. The individual tablet weights were used to calculate the weight gain's relative standard deviation (RSD). Five 20 kg tablet batches were coated with Aquarius™ Genesis yellow to a target weight gain of 3% by varying processing parameters such as drum speed, spray rate, airflow rate, and suspension concentration (Table 1). Tablets were sampled at different coating weight gains and tested for color uniformity using a reflectance spectrophotometer (DataColor 650, USA), surface roughness by optical profilometry (CHR 150, Stil, Aix-en-Provence, France, and gloss o using a Tricor gloss meter (Model 805A Gloss System, Elgin, Illinois, USA).

Results: Tablets coated with different solids contents of the suspension (20-35%) of Aquarius Genesis resulted in very short spraying times of less than 30 minutes, decreasing with an increasing solids content of the suspension and increasing spraying rate. Table 1 shows the ΔE of samples taken at different weight gains. The improvement in color uniformity shows similar behavior to the reduction in tablet weight gain RSD. All trials resulted in a ΔE < 1 already at 1.5% weight gain and a slight further decrease of ΔE to the final weight gain of 3% (Figure 1). This means that 7 minutes of spraying time in run 5 at 35% solids content resulted in acceptable aesthetics of film-coated tablets. Such results emphasize that obtaining a good color homogeneity is possible, far before achieving a 3% weight gain. These results can only be achieved using higher-efficiency coating along with coating equipment with efficient mixing. The roughness increased typically with increasing weight gain. However, since all values are below Sq=6, the tablets are regarded as smooth. As for glossiness, it typically increases with increasing weight gain. All tablets have a glossiness > 70 GU; therefore, they were regarded as glossy (Figure 2). There is no correlation between RSD and ΔE for these 5 runs. This leads to the conclusion that there is no necessity for low values of RSD to obtain tablets, which are visually perceived as similar. Values of RSD in the range of 12.7-24.7% were good enough to obtain good color uniformity.

Conclusion: In conclusion, the combination of appropriate equipment and optimized film coating systems such as Aquarius™ Genesis significantly reduced film coating process time while maintaining good visual tablet aesthetics. Tablets coated with aesthetic film coatings that aim for quality specs such as low color difference, low surface roughness, and high film coating gloss can be produced to a high quality in a very short time (well below one hour). While the measurement and indication of the color difference ΔE using datacolor analysis is an acceptable and accurate method to assess the visual quality of a coated tablet, it requires costly equipment that is not generally available at pharma companies. Alternatively, an accurate RSD determination is a good way to assess film-coated tablets.

Table 1: Coating parameters of tablets coated with Aquarius™ Genesis yellow and results.

Figure 1: Development of ΔE vs. coating weight gain

Figure 2: Roughness and gloss results of runs 1 and 5