This is a phase IV, open label, prospective, one phase pharmacokinetic and observational study.

Twenty HIV-1 infected subjects will be recruited, subjects will switch antiretroviral therapy to:

• tenofovir/emtricitabine 245/200 mg daily (Truvada™) plus
• raltegravir 400 mg twice daily On day 28, all subjects will attend for an intensive 24 hour pharmacokinetic visit.

This is a phase IV, open label, prospective, one phase pharmacokinetic and observational study.

Twenty HIV-1 infected subjects will be recruited. Eligible subjects will currently be receiving stable antiretroviral therapy with undetectable plasma HIV RNA and have no evidence of previous HIV- resistance mutations on genotypic resistance testing.

At baseline, subjects will switch antiretroviral therapy to:

• tenofovir/emtricitabine 245/200 mg daily (Truvada™) plus
• raltegravir 400 mg twice daily On day 28, all subjects will attend for an intensive 24 hour pharmacokinetic visit.

Follow up over 6 months, subjects will attend on days 14, 90 and 180 for follow up visits that will include standard safety parameters. Assessment of cardiac biomarkers at baseline and on days 90 and 180 and assessment of neurocognitive function at screening, baseline and on day 180 will also be undertaken.

Following completion of this study, subjects will recommence their usual antiretroviral treatment regimen and attend for a study follow up visit.

Inclusion Criteria:

1. HIV-1 infected males or females
2. 60 years of age or greater*
3. signed informed consent
4. willing to switch therapy as per study protocol
5. no previous exposure to raltegravir or HIV-1 integrase inhibitors
6. plasma HIV RNA < 50 copies/mL at screening and on at least one other occasion over the last 3 months
7. currently receiving a stable antiretroviral regimen with no antiretroviral drug switches for at least 3 months
8. no previous clinically-significant resistance documented on HIV-1 genotypic resistance
9. subjects in good health upon medical history, physical exam, and laboratory testing
10. BMI above or equal to 18 and below 32
11. Male subjects who are heterosexually active must use two forms of barrier contraception (e.g., condom with spermicide) during heterosexual intercourse, from screening through completion of the study.
12. Have local screening laboratory results (haematology and chemistry that fall within the normal range of the central laboratory's reference ranges unless the results have been determined by the Investigator to have no clinical significance * 50% of total enrolled cohort will be 65 years of age or over. Subsequent to 10 subjects aged between 60 and 64 recruited, only subjects aged 65 or over will be eligible.

Exclusion Criteria:

1. current alcohol abuse or drug dependence
2. positive urine drug of abuse screening
3. active opportunistic infection or significant co-morbidities
4. current disallowed concomitant medication

1 year