Effect of Single Doses of YF476 on Stomach Acidity

Inclusion Criteria: * Healthy male or female volunteers. * Aged 18-45 years. * A body mass index (Quetelet index) in the range 18.0-30.9. * Women at risk of pregnancy must use a reliable method of contraception. * No clinically relevant abnormal findings in the clinical history or physical examination at the screening assessment which could interfere with the objectives of the study or make the volunteer's participation hazardous. * No clinically relevant abnormal laboratory values at the screening evaluation, including a normal ECG. * Sufficient intelligence to understand the nature of the study and any hazards of participating in it. Ability to communicate satisfactorily with the investigator and to participate in, and comply with the requirements of, the entire study. * Willingness to give written consent to participate after reading the Consent Form, and after having the opportunity to discuss the study with an investigator or his deputy. Exclusion Criteria: * Women who are pregnant or lactating. * Clinically relevant abnormal history, physical findings, ECG, or laboratory values at the pre-study screening assessment that could interfere with the objectives of the study or the safety of the volunteer. * Presence of acute or chronic illness or history of chronic illness sufficient to invalidate the volunteer's participation in the study or make it unnecessarily hazardous. * Positive test for Helicobacter pylori. * Impaired endocrine, thyroid, hepatic, respiratory or renal function, diabetes mellitus, coronary heart disease, or history of any psychotic mental illness. * Presence or history of severe adverse reaction to any drug or a history of severe allergic disease. * Use of a prescription medicine (except oral contraceptives in females) during the 30 days before the study or use of an over-the-counter medication, with the exception of paracetamol, during the 7 days before the study. * Participation in other clinical studies of a new chemical entity or a prescription medicine within the previous 3 months. * Smokers. * Presence or history of drug or alcohol abuse, or intake of more than 28 units of alcohol weekly (for men) or 21 units of alcohol weekly (for women). * Blood pressure and heart rate in seated position at the screening examination outside the ranges 90-160 mm Hg systolic, 40-95 mm Hg diastolic; heart rate 40\_100 beats/min. * Possibility that the volunteer will not cooperate with the requirements of the protocol. * Evidence of drug abuse on urine testing. * Positive test for hepatitis B, hepatitis C, HIV1 or HIV2. * Loss of more than 400 mL blood during the 3 months before the study, e.g. as a blood donor.