This study is an open-label extension of RFSP-AMDX-2010 study for those subjects who received treatment with amdoxovir (300 mg or 500 mg twice daily) for 12 weeks and benefited from it. This study will examine the safety and efficacy of the investigational HIV drug, amdoxovir (300 mg and 500 mg bid doses; N = up to 30) in combination with zidovudine and lopinavir/ritonavir for 36 weeks.

Subjects will continue to receive either amdoxovir 300 mg twice daily or amdoxovir 500 mg twice daily, each in combination with zidovudine 300 mg twice daily and lopinavir/ritonavir (400 mg/100 mg twice daily) for additional 36 weeks.

Inclusion Criteria:

• Must have completed Study RFSP-AMDX-2010 and received treatment with amdoxovir (500 mg bid or 300 mg bid) for 12 weeks before entry into study RFSP-AMDX-2012.
• Must have maintained ≥ 1.0 log10 copies/mL from baseline at Week 12 in Study RFSP-AMDX-2010.
• Must not have had any serious adverse experience since enrollment in Study RFSP-AMDX-2010, whether or not considered to be study drug-related.

Exclusion Criteria:

• Subjects who require ongoing therapy of nephrotoxic drugs or competitors of renal excretion.
• Subjects who require therapy with hematologic, bone marrow suppressive or cytotoxic agents.
• Subjects who require medications that are highly dependent on CYP3A for clearance and for which elevated plasma concentrations are associated with life-threatening adverse events.
• Known allergy/sensitivity or any hypersensitivity to components of study drugs or their formulations.
• Women who are pregnant or breastfeeding.