Dexverapamil (R-verapamil) is an enantiomer of verapamil. R-isomer behaved as an inhibitor of multidrug-resistant protein MRP1 (involved in the cancer cell multidrug resistance phenotype). It was developed by Knoll (BASF Pharma) as a chemosensitiser and/or modulator of multidrug resistance for use in combination with cancer chemotherapy. Dexverapamil was undergoing phase II clinical studies in France, Italy, Spain, United Kingdom and the US in patients with various cancers. It was also undergoing phase I clinical trials in Japan where it was licensed to Mitsui and Mitsui Toatsu Chemicals. However, development was discontinued. Dexverapamil (R-verapamil) has been developing by AGI therapeutics for the treatment of Irritable bowel syndrome however development was discontinued.