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

Inclusion Criteria:

- Be informed of the nature of the study and have provided written informed voluntary
consent

- Be able to speak, read, and understand English;

- Be healthy males or females, of any race, between 18 and 55 years of age, inclusive;

- Have a body mass index (BMI) >18.5 and <32.0 kg/m2 and weigh 50 - 100 kg;

- Be in good general health with no clinically relevant abnormalities based on the
medical history, physical examination, clinical laboratory evaluations (hematology,
clinical chemistry, and urinalysis), and 12-lead electrocardiogram;

- Be only 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 or not post-menopausal, agree to use 2 forms
of acceptable birth control;

- Be able to communicate effectively with the Investigator and other study center
personnel and agree to comply with the study procedures and restrictions

Exclusion Criteria:

- Have previously received gefapixant;

- 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;

- 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, unless
deemed acceptable by the Investigator and Sponsor;

- 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.