This is a phase 1, single-blind, randomized, placebo-controlled, multiple ascending dose study aimed to assess the safety, tolerability, and pharmacokinetics of GS-6615 in healthy subjects.

Inclusion Criteria:

• Weight of at least 50 kg with body mass index (BMI) between 18 and 30 kg/m2
• Female subjects must be of non-childbearing potential as defined per the protocol
• Male subjects with female partners of childbearing potential must be using protocol acceptable methods of contraception
• Willing and able to comply with the requirements of the protocol and directions
• Willing to avoid consumption of grapefruit, grapefruit juice and Seville oranges
• Willing to avoid consumption of nicotine (including nicotine gum) and alcoholic beverages

Exclusion Criteria:

• Ongoing or history of any medical or surgical condition that, in the judgment of the Investigator, might jeopardize the subject's safety or interfere with the study objectives
• History of meningitis or encephalitis, seizures, migraines, tremors, myoclonic jerks, sleep disorder, anxiety, syncope, head injuries or a family history of seizures
• Any abnormal ECG findings, abnormal laboratory value, or physical examination findings at Screening judged to be clinically significant
• Any abnormal neurological examination findings at Screening that is judged as clinically significant
• Hemoglobin < 12 g/dL
• Serology test positive for HIV, or hepatitis B or C
• Positive urine drug test (including cotinine or ethanol)
• Use of systemic prescription medications or over the counter (OTC) medication, including multivitamins, and dietary and herbal supplement
• Use of any experimental or investigational drug or device within 30 days
• Female subjects who are of childbearing potential, pregnant or lactating
• Donation or loss of blood within 8 weeks and/or donation of plasma within 7 days
• History of drug or alcohol abuse
• Psychosocial or addictive disorders