Continuous Improvement in Tablet Coating and Dry Granulation - Pharmaceutical Technology

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PharmTech Europe

Continuous Improvement in Tablet Coating and Dry Granulation
Recent advances in equipment design and operation in spraying, drying, and mixing can improve the tablet-coating process.


Pharmaceutical Technology
pp. s12-s16

Tablet-coating studies

Researchers have performed various scientific studies in high-efficiency coating in solid-dosage manufacturing. These studies provide guidance for tablet-coater process improvements (1–6).

Scale-up effects on tablet abrasion during pan coating. A 2006 study investigated the influence of production scale-up on tablet abrasion in a pan coater (1). It examined how batch size during scale-up can affect the abrasion and edge-splitting of flat-faced tablets. The researchers looked at the weight loss of white tracer tablets mixed with a batch of blue-coated tablets in a laboratory-scale pan coater and a pilot-scale pan coater as a function of different pan speeds and mixing times. They observed that increasing batch size caused a decrease in weight loss due to less damage of the tablet edges. The researchers determined that a higher number of tablet impacts at the pan wall at laboratory scale compared with pilot scale might account for this outcome. This effect runs counter to the common belief that increasing batch size in scale-up leads to a higher abrasion or tablet damaging (1).

Raman spectroscopy as a PAT tool in active coating. Active coating is a film-coating application in which the drug's active ingredient is included in the coating layer. It presents manufacturers with the challenge of achieving the right amount of coating and uniformity on each dosage. To ensure the quality of each dosage, manufacturers can benefit by developing process analytical technology (PAT) that can monitor the coating process and detect the end of the coating cycle. In one study, researchers performed coating experiments using the drug diprophylline (2). They used a pan coater to coat placebo tablets and tablets containing diprophylline. During active coating, researchers recorded Raman spectra in-line. These spectral measurements were compared with the average weight gain and the amount of coated active ingredient at each point in time (2).

The chemometric model they created using Raman spectroscopy was tested by monitoring more coated batches. The research team also studied the effects of pan-rotation speed and working distance on the Raman signal and studied the resulting effect of the chemometric model. Using Raman spectroscopy as a PAT tool, they were able to determine the amount of active ingredient in the film when coated onto cores of placebo tablets and tablets containing the same active ingredient. Researchers also determined that this method can be used when changing the process parameters and measurement conditions within a restricted range, making it an appropriate PAT tool (2).

Comparing laboratory and production coating spray gun for scale-up. In a scale-up study, researchers investigated a laboratory spray gun and a product spray gun (3). They analyzed the influence of the atomization air pressure, spray-gun-to-tablet-bed distance, polymer-solution viscosity, and spray rate. The spray guns were compared based on spray width and height, droplet size and velocity, and spray density. Researchers measured spray density, droplet size, and velocity with a phase Doppler particle analyzer (3). This study gave the investigators basic information for the scale-up settings from the laboratory and production spray guns. Both were comparable with respect to droplet size and velocity, and the scale-up of droplet size can be performed by an adjustment of the atomization air pressure. Scale-up of droplet velocity can be achieved by adjusting the spray gun to tablet-bed distance. The result of the study was that the researchers' statistical model and surface plots were powerful and convenient tools for scaling up spray settings if the spray gun was changed from a laboratory spray gun to a production spray gun (3).


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