The technique of continuous coating has undergone great change since it was introduced to the pharmaceutical industry more than a decade ago, and its benefits have multiplied. At first, the method enhanced throughput and increased operational efficiencies. Manufacturers now use continuous coating to optimize process robustness and maximize the agility of manufacturing technology.

The first continuous coaters used in the pharmaceutical industry were adapted from seed-coating machines developed by Coating Machinery System  (CMS, Huxley, IA). The technology was designed to increase the size of seeds so that automated planters could plant them. The original design consisted of two stacked, perforated cylinders and multiple spray guns. Thomas Engineering (Hoffman Estates, IL) was the first company to develop a continuous coater designed specifically for the pharmaceutical industry. Shortly after Thomas introduced its coater, Vector (Marion, IA) acquired the CMS system and redesigned it for the pharmaceutical industry. The Thomas and Vector units have a throughput of roughly 200–800 kg/h.

O’Hara Technologies (Richmond Hill, Canada) entered the market later with a design similar to those of Thomas and Vector, but with a throughput of 700–2000 kg/h. All of these coaters share the same basic design. Tablets are fed into one end of a long, continuous, perforated, rotating cylinder. Next, they are conveyed through the cylinder by baffles, coated by multiple spray heads, and dried using conditioned air flow. Finally, the tablets are discharged from the unit.

Niro’s (Columbia, MD) “Supercell” machine represents a recent advancement in continuous coating. The unit is designed as a continuous cell coater and is similar in appearance to a Wurster coater. Tablets are loaded into a feed hopper. A subset of tablets (30–120 g) is fed into the cell by a vibrating loss-on-weight feeder. The unit coats this subset of tablets in 1–3 min. The Supercell coater provides a throughput of 1–4 kg/h.

The reasons to use continuous coating technology vary depending on the drug product’s phase of development. Clinical-supplies manufacturing typically requires small batches of many doses to meet trial needs and fulfill the clinical-study design. In addition, the product must be supplied quickly to accommodate the clinical-trial’s schedule. The advent of small-scale continuous coaters allows manufacturers to ensure that clinical batches match the studies’ needs. Manufacturers can thus reduce the waste that results from overmanufacturing.

In commercial manufacturing, the benefits of continuous coating technology are predominantly cost and efficiency. High throughput, large yield, and lower capital and facility expenditures are the primary advantages. Continuous coating technology has the additional advantage of featuring a smaller footprint than traditional units.

On the other hand, continuous coating does entail some startup and end-of-batch waste, which may limit the technique’s appeal in terms of yield. Process analytical technology (PAT), however, may reduce yield losses and permit an accurate, real-time assessment of coating amount and coating uniformity. The US Food and Drug Administration’s Guidance for Industry—PAT: ­A Framework for Innovative Pharmaceutical Manufacturing and Quality Assurance opened the doors for pharmaceutical companies to develop and use new processing technologies. The guidance aims to help pharmaceutical manufacturers by “providing a set of scientific principles and tools supporting innovation and a strategy for regulatory implementation that will accommodate innovation.”

The adoption of continuous coating technology has so far been limited, perhaps by the historical definition of a batch in the pharmaceutical industry and by the industry’s aversion to bringing new manufacturing approaches to regulators’ attention. With the advent of the PAT guidance and advancement of PAT technologies, pharmaceutical manufacturers will be able to take advantage of the benefits of continuous coating and still meet the need for quality.

Ruey-ching (Richard) Hwang, PhD, is a senior director of pharmaceutical sciences at Pfizer and a member of Pharmaceutical Technology’s editorial advisory board. Robert Noack is a senior principal scientist at Pfizer.