The purpose of this study is to evaluate the safety and tolerability of CMX157 and the amount of CMX157 that reaches the blood stream, the manner in which the body processes CMX157 and the time that it takes to eliminate CMX157 following one oral dose when given to healthy volunteers.

Inclusion Criteria:

1. Males or females of non-childbearing potential, 18 to 55 years of age. Males must be able and willing to use adequate contraceptive methods throughout the study.

Exclusion Criteria:

1. Currently nursing females, pregnant females, or females of child-bearing potential.
2. Hypersensitivity to tenofovir.
3. Use of any antiviral, corticosteroid, immunosuppressive, or anticoagulant prescription drug within 4 weeks prior to enrollment. Use of any other prescription drug within 14 days prior to enrollment.
4. Use of any over-the-counter medication, herbal/nutraceutical preparation, within 7 days prior to enrollment.
5. Administration of any potentially nephrotoxic drug within 14 days prior to enrollment.
6. Use of an investigational drug and/or treatment within 30 days prior to enrollment.
7. Use of illicit drugs within 6 months prior to screening and enrollment, based on history and a urine drug screen.
8. Infection with HIV, HBV or HCV.
9. History of abuse of alcohol or other substance (s) within 6 months prior to enrollment.
10. History or symptoms of cardiovascular disease, including but not limited to coronary artery disease, hypertension, congestive heart disease, cardiomyopathy, and cardiac conduction disorders.
11. History of clinically significant hypotension (including orthostatic), fainting, or lightheadedness.
12. History of gastrointestinal disease or impairment.
13. History of renal impairment or disorder.
14. History of liver disease or impairment.
15. History of cancer, except basal cell carcinoma.
16. History of pathologic bone fractures; history or risk of osteopenia
17. History of diabetes, metabolic disease, or autoimmune disease; history of immunodeficiency in healthy volunteers.
18. Acute illness or fever 38 C within 1 week prior to enrollment.
19. Supine blood pressure - systolic outside the range of 90-140 mmHg, or diastolic outside the range of 50-90 mmHg.
20. Resting heart rate > 100 or < 45 beats per minute.
21. Body Mass Index (BMI) >31 or <18, or body weight <50 kg for men and < 45 kg for women.
22. Whole blood donation within 56 days or plasma donation within 30 days prior to enrollment.