The purpose of this study is to determine if low bone mineral density (a measurement of how thick and strong bones are) improves in adults with HIV infection who switch their HIV medication tenofovir to another HIV medication raltegravir.

Hypothesis:That Bone Mineral Density (BMD) will improve in osteopenic or osteoporotic patients switching from ART including tenofovir disoproxil fumarate (TDF) and a ritonavir-boosted protease inhibitor (r/PI) to ART including RAL+r/PI.

Inclusion Criteria:

1. provision of written, informed consent

2. HIV-infected adults at least 18 years of age

3. receiving stable ART including TDF and a r/PI for the previous 6 months

4. no prior PI genotypic resistance or known replication of HIV in patients receiving a PI

5. plasma HIV RNA < 50 copies/ml for at least the previous 3 months

6. spine or neck of femur t-score ≤ -1.0 (i.e. WHO-defined osteopenia) measured by dual energy x-ray absorptiometry (DEXA)

   Exclusion Criteria:

7. participation in any other clinical trial (unless approved by the study PI)

8. use of TDF for previously active chronic hepatitis B infection

9. receiving or requiring therapy for low BMD (including prior fragility fracture)

10. using oral corticosteroids or inhaled fluticasone

11. virological failure on, or intolerance to, RAL

12. contra-indication to RAL therapy (see appendix 2)

13. breast-feeding

14. pregnancy

15. secondary, endocrinological cause of low BMD:25-hydroxy vitamin D deficiency, hypogonadism: a)symptomatic b)asymptomatic defined by total testosterone > 25% below lower limit of reference range and/or luteinizing hormone > 2 x upper limit of normal (ULN),untreated hypothyroidism or hyperparathyroidism according to local reference ranges

at 48 and 96 weeks

An adverse event (AE) is defined as any untoward medical occurrence in a clinical investigation subject administered a medicinal product and which does not necessarily have a causal relationship with this treatment.