This study will compare the blood levels of PPI-668 resulting from two different formulations - the current capsule and a new tablet.

Inclusion Criteria:

1. Have the ability to understand and sign a written informed consent form, which must be obtained prior to initiation of study procedures.
2. Must be between 18 and 55 years of age, inclusive.
3. Must be a nonsmoker. The use of nicotine or nicotine-containing products must be discontinued 90 days prior to the first dose of study drug.
4. Must have a calculated body mass index (BMI) of 18.0 to 29.9 kg/m2.
5. Must be HIV-1 antibody negative.
6. Must be hepatitis B (HBV) surface antigen negative.
7. Must be hepatitis C (HCV) antibody negative.

Exclusion Criteria:

1. Pregnant or lactating subjects.
2. Have any serious or active medical or psychiatric illness which, in the opinion of the Investigator, would interfere with subject treatment, assessment, or compliance with the protocol. This would include renal, cardiac, hematologic, hepatic, pulmonary (including chronic asthma), endocrine (e.g., diabetes), central or peripheral nervous, gastrointestinal (including an ulcer), vascular, metabolic (thyroid disorders, adrenal disease), or immunodeficiency disorders, active infection, or malignancy that is clinically significant or requiring treatment.
3. Have participated in an investigational trial involving administration of any investigational compound within 30 days prior to the study dosing.
4. Current alcohol or substance abuse judged by the Investigator to potentially interfere with subject compliance.
5. Have poor venous access and unable to donate blood.
6. Have donated blood within 56 days of study dosing.
7. Have donated plasma within 7 days of study dosing.
8. Have taken any prescription medications or over-the-counter medications including herbal products within 28 days of commencing study drug dosing with the exception of vitamins and/or acetaminophen and/or ibuprofen and/or contraceptive medications.