Dry granulation and tableting of St. John’s wort dry extract: effect of roll compaction variables, excipients, and tableting speed on granule and tablet properties

The aim of this study was to investigate the effect of roll compaction variables, various excipients, and tableting speed on the granule and tablet properties made of St. John’s wort dry extract. Three key process variables, such as roll pressure, roll speed, and milling speed were selected and their influences were studied using a factorial design. Bulk and tap density, particle size, tablet hardness and the disintegration time of tablets were significantly affected by these variables. The tablet properties such as hardness and disintegration time were considerably modified using different excipients. The effect of tableting speed on the final tablet hardness was reduced or eliminated by the application of roll compaction compared to direct compaction in the case of plastic material. Roll compaction could be successfully applied as a dry granulation method for St. John’s wort dry extract and it is suggested as a novel choice also for other herbal dry extracts to improve their undesirable properties.