The primary objectives of the study are to:

• Evaluate the potential effects of PPI-668 at steady state on the pharmacokinetic (PK) profile of midazolam following a single oral dose in human subjects.
• Evaluate the potential effects of PPI-668 at steady state on the PK profile of omeprazole following a single oral dose in human subject

Inclusion Criteria:

1. Subject or legally authorized representative signs an Institutional Review Board (IRB)-approved written informed consent and privacy language as per national regulations (e.g., Health Insurance Portability and Accountability Act [HIPAA] authorization for sites in the United States) before any study-related procedures (including withdrawal of prohibited medication, if applicable) are performed

2. Age 18 to 50 years

3. Body mass index (BMI) 18-32 kg/m2

4. Clinical and laboratory findings consistent with good health in the opinion of the investigator

5. Women of non-childbearing potential or men who agree to utilize adequate contraception throughout the study

   1. Women of non-childbearing potential must be one of the following:

      • Postmenopausal (>2 years amenorrhea and postmenopausal status confirmed by follicle-stimulating hormone levels)
      • Surgically sterile (documentation of prior tubal ligation, hysterectomy, or oophorectomy is required)

   2. Male subjects who are not surgically sterile must agree to use one of the following birth control methods if sexually active:

      • Double-barrier contraceptive (e.g., condom plus diaphragm, condom or diaphragm with spermicidal gel/foam)
      • Female partner is at least two years postmenopausal or surgically sterile

Exclusion Criteria:

1. Positive results on any of the following tests at Screening or Day -1:

   urine pregnancy (women only), urine drugs of abuse and alcohol, hepatitis B surface antigen, hepatitis C antibody, and human immunodeficiency virus antibody

2. Concurrent clinically significant medical diagnosis that would potentially interfere with the subject's study compliance or confound the study results

3. Concurrent social conditions (e.g., drug or alcohol abuse, transportation difficulties) that would potentially interfere with the subject's study compliance

4. Clinically significant illness within 30 days preceding entry into the study

5. Participation in an investigational drug study within 30 days or 5 half-lives, whichever is longer, before Screening

6. Use of prescription medications within 14 days before Day 1 and throughout the study. (The use of non-prescription or over-the-counter medications is prohibited within 7 days before Day 1 and throughout the study. This includes all herbal supplements or remedies and vitamins.)