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Tablets & Capsules January 2015 19 the conveying air. When the pails were full, the process was stopped, the pails emptied, and the process restarted. Next, the caps and bodies were loaded separately into a Wurster-type fluid-bed coater (Model GPCG-5 from Glatt, Ramsey, NJ). In the Wurster process, a stream of air moves through the product bed while the coating is sprayed; as it is applied, the stream of air dries the film coating (Eudragit L 30 D-55 from Evonik Industries, Parsippany, NJ). The target weight gains were 16 per- cent, 20 percent, and 24 percent. Table 1 shows the com- position of the enteric coating formulation. To achieve the desired weight gains, an iterative coat- ing process was used in which the actual weight gain was measured at various intervals during processing. The dif- ference between the target gain and actual weight gain was determined. Next, based on the solids content of the coating suspension and on estimates of coating efficiency, the amount of additional coating required to reach the target weight was calculated. This iterative process was repeated until the actual weight gains were within 1 per- cent of the target weight gains. Next, a 99-to-1 blend of acetaminophen and FD&C blue #1 aluminum lake was prepared in a polyethylene bag and passed through a 40-mesh hand screen. The powder was then filled into the coated capsules bearing the three different coating weights. The target weight was 505 grams. The bodies were then closed using the enteric-coated caps. Other capsule bodies bearing the three different coating weights were filled with a 99-to-1 placebo blend of microcrystalline cellulose and FD&C blue #1 aluminum lake. They too were closed using the enteric-coated capsule caps. All were visually inspected for leakage. As a positive control, uncoated capsule shells were filled with the same quantity of the acetaminophen blend as the enteric-coated capsules. Three batches of the 20-percent-weight-gain filled capsules were analyzed to evaluate batch-to-batch reproducibility. Six capsules from each batch of the coated capsules were tested for acid resistance using USP <711>: Apparatus 2 with sinkers at 50 rpm for 2 hours. The USP monograph for acetaminophen (UV detection) was used to analyze them. The uncoated filled capsules were ana- lyzed for acid resistance using the same dissolution method. Results As the images in Figure 1 show, the clear capsule caps and bodies were successfully coated with an enteric com- position (Table 1). After optimizing the equipment con- figuration and coating conditions, the coating became smooth and uniform in appearance; it was also flexible and robust enough to withstand closing after filling with- out cracking or flaking off. Figure 2 shows the average dissolution results (n = 6) of acid-resistance testing for the coated and uncoated filled capsules. For all coating weight gains, there was an aver- age release of 0 percent acetaminophen after 2 hours of exposure to an acidic medium in a dissolution bath. The results for the three batches coated to a weight gain of 20 percent demonstrated the reproducibility of the manufac- turing process and dissolution performance. Even the appearance of the three batches was the same. Figure 2 also shows the results for the uncoated filled capsules after 2 hours of exposure to an acidic medium in the dissolution bath for 2 hours. The average aceta- minophen release from them was 93 percent, confirming that the acid resistance of the coated shells was not imparted by the shells but by the enteric coating. The Table 1 Enteric coating composition Component Suspension percentage Solids percentage (w/w) (w/w) Methacrylic acid copolymer dispersion 40.8 76.1 Triethyl citrate 2.5 15.3 Glyceryl monostearate 1.0 6.2 Polysorbate 80 0.4 2.5 Purified water 55.4 (*) * Removed during processing Figure 1 Uncoated and coated capsule bodies and caps (20 percent weight gain)