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