Several comparative studies have demonstrated the effectiveness of FTC (emtricitabine, Emtriva) as an anti-HIV drug. It is active against both HIV-1 and HIV-2.

Study 301A was a double blind, multicentre study involving 571 people who had not previously taken anti-HIV treatment. Participants were randomised to receive FTC or d4T (stavudine, Zerit) in combination with ddI (didanosine, Videx / VidexEC) and efavirenz (Sustiva). After 48 weeks, 81% of the FTC group had an HIV viral load below 400 copies/ml compared to 68% of patients taking d4T, after starting with a median of 79,400 copies/ml. FTC was also superior to d4T when comparing the proportion of people achieving viral load below 50 copies/ml and the mean CD4 cell count increase^[1]. FTC continued to demonstrate superiority over d4T after 60 weeks of follow-up^[2].

In patients with experience of an anti-HIV regimen containing 3TC (lamivudine, Epivir) twice a day, switching to FTC, which is taken once a day, is as effective at suppressing viral loads as remaining on 3TC, up to four years later^[3]. However, 3TC is now licensed for once- as well as twice-daily dosing, making FTC and 3TC very similar options for use in HIV-infected patients.

Gilead also released interim results from Study 934 in August 2004, demonstrating that the combination of FTC and tenofovir (Viread) is superior to AZT (zidovudine, Retrovir) and 3TC when taken alongside efavirenz. After 24 weeks of treatment, 88% of the FTC and tenofovir patients had viral loads below 400 copies/ml, in comparison to 80% in the AZT and 3TC group. They also experienced fewer adverse events. Further data, released in October 2004, showed that treatment discontinuations due to adverse events were significantly more common in the AZT and 3TC group, suggesting that tenofovir and FTC is better tolerated during the critical early months of treatment^[4]. These results have led to Truvada becoming a rival to GlaxoSmithKline’s Combivir, a fixed-dose combination containing AZT and 3TC.

Current HIV treatment guidelines recommend FTC as a suitable NRTI for first-line regimens, when combined with AZT, tenofovir or ddI along with a protease inhibitor such as ritonavir-boosted lopinavir (Kaletra) or a non-nucleoside reverse transcriptase inhibitor (NNRTI) such as efavirenz. However, there is little evidence on the use of FTC in people who have failed previous anti-HIV treatment regimens.

Among people with hepatitis B virus, FTC produces a 2 to 3 log₁₀ reduction in hepatitis B viral load^[5][6]. FTC is also effective against HBV in patients co-infected with HIV, when included as part of an antiretroviral treatment regimen. After 48 weeks of treatment, over half of the patients treated with FTC achieve undetectable hepatitis B viral loads, a level which is similar to that in patient without HIV. HIV viral loads were also reduced to below the limit of detection in 94% of the co-infected patients^[7][8]. However, FTC is not licensed for the treatment of hepatitis B infection, and severe flare-ups of hepatitis can occur when FTC treatment is stopped in co-infected patients.