Sustained-release phenylpropanolamine hydrochloride bilayer caplets containing the hydroxypropylmethylcellulose 2208 matrix. II. Effects of filling order in bilayer compression and manufacturing method of the prolonged-release layer on compactibility of bilayer caplets

The purpose of this study was to establish the manufacturing method of the formulated bilayer caplets containing the hydroxypropylmethylcellulose 2208 (HPMC2208) matrix without lamination. In manufacturing the bilayer caplets containing the HPMC2208 (Metolose 90SH4000) matrix, some bilayer caplets were cracked. We found that cracking of bilayer caplets is not the separation of two layers, but lamination of the prolonged-release layer. It was assumed that Metolose 90SH4000 causes lamination of the prolonged-release layer. Two factors, roller compaction pressure on dry granulation of the prolonged-release layer and filling order of the prolonged-release layer in bilayer compression, were related to lamination of bilayer caplets. The compactibility of the prolonged-release layer decrease with an increase in roller compaction pressure on dry granulation. The compactibility of the prolonged-release layer manufactured by direct compression is superior to that manufactured by dry granulation. The compactibility of the prolonged-release layer in the shape of the second layer, convexo-concave, is superior to that in the shape of the first layer, convexo-convex. This is due to the fact that the density distribution inside the compact in the shape of convexo-concave was more uniform than that in the shape of convexo-convex. The manufacturing method of the formulated bilayer caplets having the prolonged-release layer whose Metolose 90SH4000 content is 60% without lamination is as follows: the prolonged-release layer manufactured by direct compression is fed as the second layer in bilayer compression.