Objective: Sennosides A and B, which are dianthrone glycosides contained in Rhubarb and Senna Leaf, exhibit laxative effect. Although a number of over-the-counter (OTC) drugs used as laxatives contain Rhubarb or Rhubarb and Senna Leaf, the total amounts of sennosides A and B are not mentioned in the package insert. To determine the total amounts of sennosides A and B in OTC drugs containing Rhubarb or Rhubarb and Senna Leaf, quantitative analyses of sennosides A and B were performed for 24 OTC drugs.
Methods: Sennosides A and B were extracted from 24 OTC drugs and quantitatively analyzed by high-performance liquid chromatography. Statistical analyses were carried out by a one-way analysis of variance followed by Dunnett's test or Tukey's test.
Results: The OTC drugs contained sennosides A and B in the range of 1.5-10 mg in the minimum daily dosage and in the range of 2.7-17 mg in the maximum daily dosage. In 11 of the OTC drugs (Products Nos. 1-5, 11, 12, and 15-18), the maximum daily dosage contained almost equal or higher amounts of sennosides A and B compared to that in a tablet of the prescription medicine Pursennid® 12 mg. Furthermore, the amounts of sennosides A and B in the maximum daily dosage were significantly higher in products Nos. 1 and 11 and lower in products Nos. 8-10, 14, and 20-24 compared to those of a tablet of Pursennid® 12 mg.
Conclusion: Although some OTC drugs have the same Rhubarb content, the total amounts of sennosides A and B can vary. Thus,there is no correlation between the Rhubarb content and total amounts of sennosides A and B. This is because of the inconsistent quality of Rhubarb and/or the differences in the manufacturing methods of the OTC drugs containing Rhubarb. Because the total amounts of sennosides A and B cannot be estimated based on the Rhubarb content, a constipated patient should start taking an OTC drug containing Rhubarb at the minimum daily dosage. It is also recommended that the total amounts of sennosides A and B are mentioned in the package insert of OTC drugs containing Rhubarb or Rhubarb and Senna Leaf.
