Semi-Continuous Coating

Aspirin tablets (325 mg) were used as the coating substrate. The coating was a fully formulated aqueous enteric coating system, Acryl-EZE^® (Colorcon Inc.), prepared at a solids concentration of 20%. The coating trial was conducted with a batch size of 3 kg and the final target weight gain (WG) was 12% w/w.

Tablets were automatically fed into a single coating module and automatically discharged at the completion of each coating cycle in a semi-continuous process. 

Coated tablet samples were withdrawn from the process at 5, 6, 8 and 10% applied WG. Enteric performance was evaluated using USP Dissolution Apparatus 1 at 100 RPM. Enteric coated tablets (n = 6) were tested in 0.1N HCl for 2 h and then immediately transferred into phosphate buffer (pH 6.8) for dissolution and drug release testing.

Results

The enteric coated tablets were smooth and glossy and free from any apparent defects. The color uniformity of the tablets was very good — as expected at the higher weight gains sampled for enteric testing. Dissolution testing demonstrated robust enteric coating performance: 5% WG samples exhibited no drug release at pH 1.2, and a release of greater than 90% in 45 minutes in pH 6.8 buffer.

Slight differences in the rate of drug release were observed in the buffer phase depending on the applied coating WG. As expected, a higher WG resulted in a slightly slower release; yet, all samples reached >90% release within 20 minutes. The total coating time to reach 12% WG was 30 minutes. Passing enteric results were achieved in 12.5 minutes of coating at 5% WG, indicating excellent coating uniformity. This early protection and the absence of any visible tablet edge defects indicates low tablet stress in this dynamic process.