- Subjects who are unlikely to complete the 48 week trial period. Currently active opportunistic disease or documented wasting syndrome. Currently receiving chemotherapy for malignancy. Subjects who are unlikely to retain viral response after switching based on treatment or transmission history. Currently receiving an insulin sensitising agent (glitazone or metformin). Anabolic steriods in the last 16 weeks other than testosterone at replacement doses (less than or equal to 250 mg/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 may be included). Current alcohol or illicit drug use which may interfer 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 labeling will result in clinically significant interactions with tenofovir or abacavir. Pregnant or breast feeding. Previously received more than 3 months zidovudine monotherapy.