metabolite. This may be mediated through genetic differences in the gene that encodes for the metabolic enzyme CYP2C19. For example, people that are poor CYP2C19 metabolizers (i.e. their version of CYP2C19 is less effective than average) will have trouble metabolizing rabeprazole, allowing the active rabeprazole to stay in the body, where it can exert its effect, longer than intended. Conversely, extensive CYP2C19 metabolizers (i.e. the average metabolic capacity of CYP2C19) will extensively metabolize rabeprazole, as expected. The poor metabolizing CYP2C19 phenotype is found in roughly 3–5% of Caucasian people, and in 17–20% of people of Asian ancestry. In a study on men of Japanese ancestry, this has translated to an average increase of total drug exposure by 50–60% compared to men in the United States. However, rabeprazole's metabolism is primarily non-enzymatic (it is often inactivated chemically, without the participation of the body's natural drug metabolizing enzymes). Therefore, while a person's CYP2C19 phenotype will affect rabeprazole's metabolism, it is not expected to dramatically affect the efficacy of the medication. Chemistry Rabeprazole is classified as a substituted benzimidazole, like omeprazole, lansoprazole, and pantoprazole. Rabeprazole possess properties of both acids and bases, making it an amphotere. The acid dissociation constant (pKa) of the pyridine nitrogen is about equal to 5. Synthesis The above synthesis pathway begins with 2,3-dimethypyridine N-oxide (1). Nitration of 2,3-dimethylpyridine N-oxide affords the nitro derivative (the addition of NO2) (2) The newly introduced nitro group is then displaced by the alkoxide from 3-methoxypropanol to yield the corresponding ether (3). Treatment with acetic anhydride results in the Polonovski reaction. Saponification followed by treatment with thionyl chloride then chlorinates the primary alcohol (5). Reaction with benzimidazole-2-thiol (6) followed by oxidation of the resulting thioether to the sulfoxide yields the final product: rabeprazole (8). Physiochemical properties Rabeprazole is characterized as a white to yellowish-white solid in its pure form. It is soluble in a number of solvents. Rabeprazole is very soluble in water and methanol, freely soluble in ethanol, chloroform, and ethyl acetate, and is insoluble in ether and n-hexane. It is unstable under humid conditions. History Rabeprazole was first marketed in Europe in 1998. In 1999, one year later, rabeprazole was approved for use in the United States. Development Developed by Eisai Medical Research by the research names E3810 and LY307640, the pre-investigational new drug application was submitted on October 28, 1998. The final investigational new drug application was submitted August 6,