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