Issue link: https://www.e-digitaleditions.com/i/1371139
Tablets & Capsules May/June 2021 13 But what constitutes good coating uniformity? For drug-layering processes, uniformity targets are obviously driven by a need to meet drug-content regulatory require- ments. For modified-release products, while the targets may be less well defined, the goal is ultimately to achieve consistent and reproducible functionality. has been designed as a key element of the company's con- tinuous ConsiGma manufacturing process. The Omega coater is somewhat unique in design because: • The batch capacity is typically only 3 to 4 kilograms; • The batch coating time is around 6 to 8 minutes; • Two machines operate in parallel—while one is coating, the second is filling to start the next coat- ing cycle; • Pan speed, process airflows, and inlet temperatures are typically higher than for a normal aqueous coat- ing process; and • The high pan speed and negative pressure inside the coater hold the tablets stationary against the pan wall until they are dislodged by means of an air knife at approximately the 11 o'clock position, after which the tablets cascade essentially in free-fall mode through a spray zone created by an upward-pointing spray nozzle. Figure 5 shows an example of the GEA setup, which can typically achieve throughput rates in the range of about 10 to 100 kg/h, depending on the coating formulation type. Table 2 shows the effect of coating solids on achievable throughput rates for this process. Improved coating uniformity: Myth or reality? The uniformity of the coating distribution onto the sub- strate (whether tablets, capsules, or multiparticulates) can be an important quality attribute. For purely cosmetic tablet coatings, little attention is paid to coating uniformity if all tablets appear to be the same color (for color-coated prod- ucts) at the end of the process. For modified-release coatings (barrier coatings, taste-masking coatings, delayed-release coatings, and controlled-release coatings) and situations where drug-layering is a requisite part of the process, greater attention must be paid to achieving good coating uniformity. Figure 5 Typical GEA Omega coating process setup Automated tablet feed hopper Fluid delivery setup Automated tablet discharge hopper 160-millimeter wheel Pan is filled with tablets Tablet stick to wall as pan rotation accelerates to 115 rpm Pan rotation slows to about 88 rpm, raising air-knife pressure and causing tablets to cascade through spray zone Table 2 Impact of coating solids percentage on tablet throughput rates using Aquarius Genesis (Ashland) coating and a GEA Omega coater (data courtesy of Ashland) Solids content (% w/w) of coating suspension Target weight gain (%) Spray rate (g/min) Coating suspension applied (g) Coating time per cycle (min) Setup time* (min) Throughput rate (kg/h) for twin wheel configuration 25 3 60 360 6.0 2 60 25 3 80 360 4.50 2 80 30 3 60 300 5.0 2 72 30 3 80 300 3.75 2 96 32.5 3 60 277 4.62 2 78 32.5 3 80 277 3.46 2 104 35 3 60 257 4.28 2 84 35 3 80 257 3.21 2 112 * Time to load, preheat, dry, and discharge