Rapid Screening Phenotype Test To Evaluate CYP 2C19 Enzyme Activity Using Stable Isotope [13C]Pantoprazole

The goal of this study is to develop a quick and reliable method that will diagnose hepatic CYP2C19 function and could be used routinely in clinical practice. Specifically, we propose to test pantoprazole - 13C as a probe for determining CYP2C19 phenotype. Pantoprazole, 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-2-pyridyl)-methyl]sulfinyl]-1H -benzimidazole, is a substituted benzimidazole sulfoxide and a selective and long-acting proton pump inhibitor. This drug is widely used clinically in the treatment of severe gastroesophageal reflux disease, and for treatment of duodenal and gastric ulceration. Pantoprazole is extensively metabolized in the liver, with almost 80% of an oral or intravenous dose is excreted as metabolites in urine. The main metabolite is formed by O-demethylation at the 4-position of the pyridine ring by CYP2C19, followed by conjugation with sulphate (M2), while pantoprazole sulfone formed by CYP3A represents a minor metabolic pathway(20). The critical role of CYP2C19 in the in vivo clearance of the drugs is further demonstrated by the fact that healthy volunteers that are PMs of this enzyme achieve approximately 6-fold higher pantoprazole exposure than those who are extensive metabolizers of CYP2C19(20). This concept proposal exploits the use of the 13C-label that is incorporated at the O-methyl site of pantoprazole, which specifically designed for the CYP2C19-mediated O-demethylation (Figure 1). Then, during catalysis, CYP2C19-pantoprazole reaction in the liver results in the release of 13CO2 which is then eliminated from the body via the lung expired breath. The subsequent quantification of 13CO2 allows indirect determination of the hepatic CYP2C19 enzyme and thus the pharmacokinetics of its substrates. The salient features of the 13C-breath test means that this test would be non-invasive, non-radioactive, safe and simple. The protocol in general can be performed rapidly (one hour or less after pantoprazole administration) and can be determined directly at the point of care (e.g., hospitals and physicians' offices) using relatively inexpensive instrumentation (UBiT-IR300IR spectrometer; Meretek), and patients do not require waiting for hours or days for diagnostic results. This test may be particularly important to probe the activity of CYP2C19 for infants, children, pregnant and lactating women, seniors averse to the use of needles or in poor health and subjects scared of blood draws.

Inclusion criteria

• Asian male or female subjects between 18 and 49 years of age, who are in good physical health with no significant medical problems or laboratory test abnormalities. Subjects should have normal liver and kidney function.
• Subjects with BMI <30 which will be determined by Metropolitan height and weight tables. Subjects must weigh at least 110 pounds.
• Subjects must agree to refrain from taking any prescription and over-the-counter medications, as well as any herbal medications one week before the start of the study and during the study period.
• Subjects must agree to refrain from consuming alcohol 48 hours before the start of the study and during the study period.
• Subjects must be capable of satisfying protocol requirements and be able to sign written informed consent.

Exclusion criteria

• Subjects who have a history of intolerance or allergy to the study drug: pantoprazole.
• Subjects who have donated blood within the last 60 days of the screening visit or plan to donate blood during the course of the study or within 60 days after study completion.
• Subjects who have had treatment with any investigational drug within the past 30 days.
• Subjects who have used illegal drugs within three months prior to enrollment.
• Female subjects currently taking oral contraceptive birth control pills and who are unwilling or unable to stop oral contraceptives and use a barrier contraceptive method (such as condom, contraceptive foams, etc.) starting from the time of screening phase to the completion of the study.
• Female subjects who are pregnant or lactating.
• Subjects who are unreliable in the opinion of the study physician.