A Multiple-Dose Pharmacokinetics Study of Two Gefapixant (AF-219/MK-7264) Formulations

Inclusion Criteria: * Must be informed of the nature of the study and have provided written informed voluntary consent; * Able to speak, read, and understand English; * Healthy males or females, of any race, between 18 and 55 years of age, inclusive; * Body mass index (BMI) \>18.5 and \<32.0 kg/m2 and weigh 50 - 100 kg; * In good general health; * Non-smokers or intermittent (social) smokers for at least 5 years, and able to refrain from smoking (or using nicotine) while in confinement; * If a female of child-bearing potential (i.e., have not undergone a hysterectomy or bilateral oophorectomy) or not post-menopausal (defined as no menses for at least 12 months), agree to use 2 forms of acceptable birth control; or if a male, they and/or their partner of child-bearing potential agree to use 2 forms of acceptable birth control; when in line with the preferred life style of the subject, true and complete abstinence (not periodic abstinence) is acceptable; Exclusion Criteria: * Any disease or condition that might affect drug absorption, metabolism, or excretion or clinically significant cardiovascular, hematological, renal, hepatic, pulmonary, endocrine, gastrointestinal, immunological, dermatological, neurological, or psychiatric disease; * Clinically significant illness or clinically significant surgery within 4 weeks before the administration of study medication; * Any past sinus surgery, upper respiratory tract infection within 2 weeks before dosing, or history of hay fever during the time of the year that dosing will be taking place; * History of GERD, heartburn, or nausea more than once a month, or any similar symptoms requiring the regular use of antacids, or any use of H2 histamine blockers or proton pump inhibitors within 12 months of Screening; * Have a positive screening test for Helicobacter pylori; * QTcB \>450 msec in males or \>470 msec in females; * Known or suspected hypersensitivity or allergic reaction to any of the components of gefapixant or omeprazole capsules; * If female, is pregnant or breast feeding, or has a positive pregnancy test pre dose; * Blood loss or blood donation of \>550 mL within 90 days or plasma donation \>500 mL within 14 days before administration of the first dose of study drug; * Chronic use of any systemic medications (other than allowable oral and implanted contraceptives and with the exception of vitamins taken at standard supplement doses); use of a drug therapy (including herbal preparations, e.g., St. John's wort) known to induce or inhibit hepatic drug metabolism within 30 days before the first dose of study medication; or use of any medications \[prescription or over the counter (OTC)\], including antacids, high dose multivitamins, nutritional supplements, and herbal preparations, within 14 days before the first dose of study drug; * Past or current history or evidence of drug or alcohol abuse, regular use of more than 2 units of alcohol per day (1 unit of alcohol = 150 mL of wine, 360 mL of beer, or 45 mL of alcohol 40%), use of any recreational soft drugs (e.g., marijuana) within 3 months of screening, use of any hard drugs (such as cocaine, phencyclidine (PCP), and crack) within 1 year of screening, and/or a positive screen for substances of abuse or alcohol at screening or pre dose; * Ingestion of grapefruit or grapefruit juice within 48 hours before dose administration; * Positive screen for hepatitis B surface antigen (HBsAg), hepatitis C antibody, or human immunodeficiency virus (HIV) antibody; * Receipt of an investigational product or device, or participation in a drug research study within a period of 30 days (or 5 half lives of the drug, whichever is longer) before the first dose of study medication; * Receipt of an investigational immunomodulator or monoclonal antibody within 180 days (or 5 half lives, whichever is longer) before the first dose of study medication.