A Phase 1 Study of Novel GS-9973 Tablet Formulations to Evaluate the Effect of Acid Reducing Agents, Relative Bioavailability, and Food Effect on GS-9973 Pharmacokinetics

Inclusion Criteria:

- Have the ability to understand and sign a written informed consent form, which must
be obtained prior to initiation of study procedures

- Must have a body mass index (BMI) range of approximately 19 to 30 kg/m2

- Must have a minimum weight of 45 kg

- Females of childbearing potential must have negative serum pregnancy tests at
screening and baseline and must practice at least 1 reliable method of contraception
as defined by the protocol

- Female subjects who utilize hormonal contraceptive as 1 of their birth control
methods must have used the same method for at least 3 months prior to study
dosing

- Male subjects must agree to use condoms during heterosexual intercourse and avoid
sperm donation from Day -1 until 90 days following the last dose of study medication

- Must refrain from blood donation throughout the study period

- Must, in the opinion of the Investigator, be in good general

- Must be a non- or light smoker, eg, less than 10 cigarettes per day

Exclusion Criteria:

- Pregnant or lactating subjects

- Use of prescribed or over-the-counter medications that affect gastric pH

- History of severe peptic ulcer disease, GERD, or other diseases requiring
prolonged(>6 weeks) medication or surgical therapy to modify gastric pH

- Have a history of clinically significant cardiac abnormalities or presence of
clinically significant abnormality on 12-lead ECG.

- Have a history of any cancer requiring systemic chemotherapy or radiation

- Have a history of bleeding disorders

- Have a history of liver disorders

- Current acute infection or history of acute infection within 7 days

- Have a recent history of alcohol or illicit drug abuse and/or have a positive test
for selected drugs of abuse

- Have a positive hepatitis screen or positive Human Immunodeficiency Virus antibody
test

- Have participated in another clinical trial within 28 days

- Have received transfusion of blood or plasma products within 6 months

- Have donated > 500 mL blood within 56 days

- Are unable or unwilling to comply with study restrictions, return for follow-up
appointments, or other considerations, which in the opinion of the Investigator,
would make the candidate unsuitable for study participation

- Current or historical medical condition that is deemed to be of medical significance
by the Investigator

- Have used prescription medications, over the counter products, herbal remedies and
nutritional supplements within 7 days