Study to Evaluate Changes in Limb Fat When Switching From a Thymidine Analogue

Inclusion Criteria: * Subjects who are male or female \> 18 years of age * Subjects who are HIV-1 infected as documented by a licensed HIV-1 antibody ELISA * Female subjects of childbearing potential must have a negative serum pregnancy test (beta-HCG) within 28 days of trial day 1. Women of childbearing potential must agree to use a barrier method of contraception * Female subjects must not be pregnant or lactating * Subjects who in the opinion of the investigator have the ability to understand and provided written informed consent to participate in the trial * Subjects who in the opinion of the investigator have clinical lipoatrophy at \> 1 body/facial site * Subjects currently receiving nucleoside analogue regimen including stavudine (d4T) or zidovudine (ZDV) * Subjects who are stable on current therapy for \>16 weeks * Subjects with no prior exposure to tenofovir, abacavir, or adefovir * Subjects with no known K65R, 69S mutations or 3 or more thymidine analogue mutations * Subjects with documented viral load \<50 copies/ml on 2 consecutive occasions including most recent clinic attendance Exclusion Criteria: * Subjects who in the investigator's opinion are unlikely to complete the 48 week trial period * Currently active opportunistic disease or documented wasting syndrome * Currently receiving chemotherapy for malignancy * Subjects who in the opinion of the investigator are unlikely to retain viral response after switching based on treatment or transmission history * Currently receiving an insulin sensitising agent (glitazone or metformin) * Anabolic steroids in the last 16 weeks other than testosterone at replacement doses (\<250mg/2 weekly) * Growth hormone use in the last 16 weeks * Statin therapy (HMG CoA reductase inhibitor) commenced in the last 16 weeks (patients stable on statins my be included) * Current alcohol or illicit drug use which, in the opinion of the investigator, may interfere with the subjects' ability to comply with the dosing schedule and protocol evaluations * Receiving concurrent medications that - in the opinion of the investigator and according to drug product labelling - will result in clinically significant interactions with tenofovir or abacavir * Pregnant or breast feeding * Previously received more than 3 months zidovudine monotherapy