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

Inclusion Criteria: 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