Safety and Antiviral Study of ACH-126, 443 (Beta-L-Fd4C) in the Treatment of Adults With HIV Infection and Modestly Detectable Viral Load.

• Adults ≥18 years of age
• Receiving a stable triple combination antiretroviral regimen including 3TC, one other NRTI and either an NNRTI or a protease inhibitor for at least 4 months (16 weeks)
• Demonstration of initial viral suppression and subsequent rebound to be defined as an initial virological drop of at least 0.5 Logs on a 3TC-containing regimen
• Plasma HIV RNA level > 1000 and \< 30,000 copies/mL on two occasions
• Genotypically documented M184V variant of HIV RT
• Clinically stable HIV status with no AIDS-defining events
• CD4 > 200 cells/mm3
• Basic hematologic and chemistry parameters within acceptable limits (defined in protocol)
• All women of child bearing potential must have a negative serum or urine pregnancy test (minimum sensitivity of 25 IU/L of b-HCG) within 72 hours prior to the start of study medication
• No active opportunistic infection requiring treatment
• Subject must be able to provide written informed consent
• Baseline laboratory values measured within 28 days of initiating study drug as follows:
• HGB≥9.0g/dl or HCT≥27% (in the absence of blood transfusions or erythropoietin treatment in the preceding two weeks
• Absolute neutrophil count≥1000 cells/mm(\^3) (in the absence of on-going G-CSF therapy
• Platelet count ≥75,000/mm(\^3)
• AST \<7.0 times the upper limit of normal
• ALT ,7.0 times the upper limit of normal
• Serum creatinine \<1.1 times the upper limit of normal

Exclusion Criteria

• Evidence of active HBV infection as demonstrated by HBsAg positivity
• Hepatitis C co-infection
• Concurrent systemic antiviral treatment
• Previous therapy with agents with significant systemic myelosuppressive or cytotoxic potential within 3 months of study start or the expected need for such therapy at study start.
• Alcohol abuse
• Pregnancy or breast-feeding
• Inability to tolerate oral medication
• AST > 7.0 times the upper limit of normal
• ALT > 7.0 times the upper limit of normal
• Any clinical condition or prior therapy that, in the Investigators opinion, would make the subject unsuitable for the study or unable to comply with the dosing requirements.
• Use of any other drug or substance with anti-HBV activity