A Study to Assess the Effect of Intragastric pH and Fasting on the Pharmacokinetics of Gefapixant (AF-219/MK-7264)

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 for at least 5 years;

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;

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 >460 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; use of a drug therapy known to induce or inhibit
hepatic drug metabolism within 30 days before the first dose of study medication; or use
of any medications 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, 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 urine cotinine test at Screening or Day 1 pre dose;

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