Keep it moving Literature
New coating technology increases the efficiency of tablet production

The new continuous Supercell Coater from Niro Pharma Systems shows that there is still potential for improvement even in a well-established process. When utilized to its fullest, the coater can be used to create a continuous flow of tablets from the tablet press right on through coating and blistering.
Dr. Harald Stahl
Tablet coating running in batch mode is often performed between the continuous tablet production process and packaging (e.g. into blister packs). This inevitably interrupts the continuous flow of tablets after the pressing step, and this is less than ideal from the production engineering and cost standpoint. When a continuous coater is used, the tablet press, continuous coater and blister line can be run in-line. This saves time, space, production personnel and ultimately money.

The right amount of coating

Conventional coating methods often have the disadvantage that the coating on the tablets is not uniform. However, to ensure that the coating has the intended effect, the correct amount of coating must be applied to each and every tablet. The common continuous processes, where blades move the tablets from the inlet to the discharge point, cannot deliver this level of uniformity due of differences in residence time. Some tables move through the apparatus more quickly than others and do not pick up sufficient coating. An excessive coating is applied to other tablets which remain in the apparatus too long. To address this problem, Niro Pharma Systems has taken a different approach during the development of its Super Cell Coater. Tablet cores coming from the continuous production process are divided into micro batches (30–120 grams) and fed into the apparatus. The coating process takes one to five minutes depending on the desired coating thickness. If the capacity of the coater is not sufficient, several coaters can be connected in parallel and loaded serially.

Fluidized bed

The system is based on fluidized bed technology with a patented air diffuser [1,2]. A large volume of air is introduced into the process chamber to enhance drying performance. As a result, the engineers were able to achieve very high spray rates and short coating times. It is critical that the process air which flows in at high velocity merely fluidizes the tablets and keeps them rotating without creating vertical momentum. Otherwise the tablets would collide at the top of the process chamber causing damage to the tablets and the coating.

The desired quantity of tablets is assembled at the top of the coater. Once the tablets are introduced into the actual process chamber, a nozzle mounted on the bottom sprays coating fluid onto the tablets. The solution/suspension is stored in a separate container and constantly kept in motion through a ring loop to prevent demixing caused by separation of the suspended particles. The correct amount of coating is supplied from the ring loop to the metering pump for every sub-batch, and it is then applied at the specified rate. Several independent dosing systems can be used in series to apply a multi-layer coating. Following spraying and an additional drying step which takes only a few seconds, the tablets are removed from the process chamber through an immersion tube. Water or a suitable solvent is then sprayed into the process chamber to prevent the nozzle from blocking up. The next micro batch is then loaded and coated. The process can be run continuously and unattended for any number of micro batches. Besides the possibility of deploying the Super Cell Coater to configure a fully continuous, integrated tablet line which includes the pressing, coating and blister packing steps, the functional design of the machine can be exploited in other applications.

Hiding the taste

The coating on a tablet prevents contact with the active ingredients which often taste bitter. If the coating is applied with a conventional drum coater, there is always the risk that abrasion will release some material containing the active ingredient regardless of the amount which is applied. Some of this material will be deposited in the outermost layer and will significantly reduce the taste masking effect. Supercell coating technology eliminates this risk, because high velocity air extracts the dust which is then removed by the filters. Trials with tablets which contain quinine sulphate, which has a very unpleasant taste, have shown that the new coating technology is superior to conventional methods.

Moisture protection

Because the residence time in the process chamber is very short and the coating fluid which is sprayed is immediately vaporized, a coating can also be applied to products which are temperature or moisture sensitive, like for example even effervescent tablets with an aqueous Opadry 2 suspension.

Deposition of active ingredients

There are a number of medications on the market where a layer of active ingredient, which is quickly released, is deposited on a core of the same ingredient which is released slowly. However, there has recently been a trend to deposite different active ingredients in the layers. This requires significantly better reproducibility in the amounts which are applied per tablet. The accuracy of conventional drum coater is normally not sufficient [3,4]. Birkmire and Liew [5] were able to apply less than 200 micrograms per tablet with a relative standard deviation of under five percent.

Simplified screening

Due to the enormous reduction in drying time (several minutes per micro batch) compared to drum coaters, Supercell coating technology can be used to quickly screen a variety of recipes and process parameters. The volumes of the substance which are produced (30 – 120 grams per micro charge) are sufficient for subsequent analytic characterization. This in turn facilitates upscaling. You simply increase the number of micro batches or if necessary the number of cells.

Summary

Due to the patented design, the Supercell Coater which has been developed by Niro Pharma Systems has the capability to coat tablets on the fly as soon as they leave the tablet press. The coater is also ideal for taste masking, or for temperature or moisture sensitive tablets. Compared to other coating methods, the amount of coating applied to the tablet is much more uniform. Because batch times are very short, the system is also suitable for recipe and process development.n

[1] Walter, K.T. and Neidlinger, M.A., Apparatus for Coating Tablets, US Patent, 6,209,479 (2001)

[2] Walter, K.T. and Neidlinger, M.A., An Apparatus and a Process for Coating Tablets, European Patent, 1 140 366 (2000)

[3] Tobiska, S. and Kleinebudde, P., Coating Uniformity: Influence of Atomising Air Pressure. Pharm. Dev. Tech., 8(1), 39-46 (2003)

[4] Tobiska, S. and Kleinebudde, P., Coating Uniformity and Efficiency in a Bohle Lab-Coater using Oval Tablets, Eur. J. Pharm. Biopharm., 56. 3-9 (2003)

[5] Birkmire, A. P. and Liew, C., An Accurate Method of Coating Tablets with Active Pharmaceutical Ingredients, European Coating Symposium 9 (2003)