Apricitabine (AVX754)—an experimental nucleoside reverse transcriptase inhibitor (NRTI)—can be used safely and effectively for nearly two years in combination with other antiretrovirals, according to a press release by Avexa Limited, the drug’s developer.

Apricitabine is chemically very similar to lamivudine (found in Epivir, Combivir and Trizivir) and emtricitabine (found in Emtriva, Truvada and Atripla), but it was designed to work against HIV that has become resistant to those two drugs. To test apricitabine’s effectiveness and safety, Avexa launched a Phase IIb study in 2006 that compared two doses of apricitabine with Epivir in people who had developed the signature lamivudine resistance mutation, M184V. After six months, everyone in the trial took the higher dose of apricitabine, 800 milligrams, and they have been followed ever since.

Avexa reports that at 96 weeks, 87 percent have maintained undetectable HIV levels. No one has withdrawn from the study due to side effects, nor have researchers reported any serious side effects of apricitabine. Avexa is currently conducting an ongoing Phase III study of apricitabine.