Background: Emtricitabine (Coviracil, FTC) is a cytosine analog that has demonstrated superior antiviral activity and safety compared to stavudine in a randomized, double-blind clinical trial. FTC-303 was a randomized, 48-week (wk), open label equivalence trial in which patients (pts) with HIV-1 RNA ≤ 400 copies/mL either continued their 3TC-containing regimen or switched 3TC 150 mg BID to FTC 200 mg once daily. Pts with plasma HIV-1 RNA ≤ 400 copies/mL at week 48 of FTC-303 were offered FTC as part of their HAART regimen in protocol FTC-350.

Methods: Adverse event (AE), clinical laboratory, and HIV-1 RNA data were collected every 4 wks through wk 48 and then every 8 wks thereafter in FTC-350. Virologic failure (VF) was defined as HIV-1 RNA > 400 copies/mL on two consecutive visits and was assessed using the Kaplan-Meier (KM) estimator.

Results: Out of 294 total, 227 (77%) pts randomized to FTC in FTC-303 had HIV-1 RNA ≤ 400 copies/mL at wk 48. Of these, 215 elected to continue FTC in FTC-350; 152 of 294 (51%) maintained suppression of HIV-1 RNA ≤ 400 copies/mL and 139 (47%) ≤ 50 copies/mL through wk 120 (2.3 yrs). The KM probability of VF at wk 120 was 12 %. Most AEs were mild or moderate; the annualized incidences of drug-related severe or potentially life threatening AEs were 3% and < 1%, respectively. The annualized incidences of Grade 3 and Grade 4 laboratory abnormalities were 11% and 10%, respectively. Of these, asymptomatic and transient elevations in CPK accounted for more than 2/3 of the overall Grade 4 incidence.

Conclusions: HIV-infected adults on a stable HAART regimen containing Lamivudine (3TC) who switch 3TC 150 mg BID to FTC 200 mg once daily have excellent safety, tolerability, and durable suppression of plasma HIV-1 RNA through 120 wks.