[Herbological studies on combination of rhubarb and mirabilite]

In traditional Chinese medicine, it has long been thought that the medicinal effect of a crude drug can be modified by combination with other crude drugs. One well-known example is the combination of mirabilite (a purgative) and rhubarb (an anti-inflammatory and essentially anti-blood stasis drug). One description in the medicinal literature states that mirabilite has to be added after rhubarb has been decocted. Another description states that rhubarb needs to be processed with liquor when both crude drugs are used together. However, the reason why rhubarb and mirabilite are used together, why mirabilite is added afterward, and why rhubarb needs to be processed with liquor have not been elucidated completely. Therefore, we performed a herbological study and found that rhubarb is expected to act as a purgative while mirabilite is expected to act as a stool softener when they are used together. We also found that they are used together to speed up the onset of a purgative effect in each other. Secondly, we decocted rhubarb (unprocessed or liquor-processed) and mirabilite together, and analyzed the content of principal compounds. We found that sennoside and anthraquinone contents of the rhubarb decoction were reduced by adding mirabilite. However, when mirabilite was added after rhubarb had been decocted, the decrease was smaller than when they were put in water at the same time. In addition, the decoction of liquor-processed rhubarb showed low sennoside content. Therefore we conclude that mirabilite is added after rhubarb has been decocted to prevent the decrease of active compounds, and we consider that unprocessed rhubarb is suitable for expecting a purgative effect.