Capsules with prolonged action. II. Capsule filling by a gelation process.

A new formulation for manufacturing sustained-release soft gelatin capsules was investigated. It consists of a gel solid formed by ethylcellulose and sesame oil and 20 to 35% polyethylene glycol 400 for the enhancement of drug release. Citric acid triethylester (Citroflex-2) makes it possible to combine sesame oil with polyethylene glycol. By recording the rheological behavior at various temperatures, the thixotropic properties of the mixture that leads to the gel-forming process were ascertained. The ideal temperature for filling into soft gelatin capsules can also be determined by this method. The release profile of codeine dissolved or suspended in the mixture shows the typical matrix-type release. In contrast, a high amount of theophylline suspended in the carrier system yields an erodible matrix with an almost-constant release rate.