The herbal medicine rikkunshito exhibits strong and differential adsorption properties for bile salts.

Anti-secretory drugs, particularly proton pump inhibitors (PPIs), are the preferred treatment agents for patients with gastroesophageal reflux disease (GERD). However, refractory GERD, which may manifest as an incomplete or lack of response to PPI therapy, is common. Despite the administration of PPIs for symptomatic control, duodenogastroesophageal reflux (DGER) containing bile is successfully controlled in only one-third of patients. It has previously been reported that the traditional Japanese herbal medicine rikkunshito, which has a prokinetic action on gastric emptying, exhibits clinically therapeutic effects against GERD and DGER that does not respond to PPIs. However, the precise mechanisms responsible for the effects of rikkunshito are still unknown. It has been suggested that the cytotoxicity of the bile salts in the gut lumen is important in GERD and DGER. The aim of the present study was to investigate whether rikkunshito is able to adsorb bile salts through the mechanism by which it ameliorates the symptoms of GERD and DGER. The binding capacities of rikkunshito for bile salts were measured using Langmuir's method. The morphology of rikkunshito was also observed by light microscopy. Rikkunshito strongly adsorbed bile salts. The binding capabilities of rikkunshito were far beyond those of a typical dietary fiber, α-cellulose, or an oral adsorbent. In addition, rikkunshito had higher binding capacities for hydrophobic bile salts as compared with hydrophilic bile salts. In conclusion, rikkunshito has a great capacity to adsorb bile salts. This may be part of the mechanism(s) responsible for the therapeutic effects of rikkunshito in patients with GERD and DGER.