New data presented last week at the XVII International AIDS Conference (IAC) in Mexico City support the continued development of IDX899, an experimental non-nucleoside reverse transcriptase inhibitor (NNRTI) being developed by Cambridge, Massachusetts-based Idenix Pharmaceuticals. According to Carlos Zala, MD, of the University of Buenos Aires who presented the Idenix study results at IAC, IDX899 reduced viral load by an average of 1.8 log copies after seven days of treatment using different doses of the drug, compared with a 0.05 log viral load increase among those receiving a placebo. The drug was also found to be generally safe and well tolerated.
IDX899 is a potent NNRTI that has demonstrated activity, at least in test tube studies, against drug-sensitive "wild-type" HIV and virus with mutations conferring resistance to approved NNRTIs. Dr. Zala also reported that the compound has a high genetic barrier to resistance. In other words, compared with NNRTIs such as Sustiva (efavirenz) and Viramune (nevirapine), it may take HIV longer to develop drug-resistant mutations.
Data also suggest that IDX899 can be taken once a day.
Zala and his colleagues' Phase I/II clinical trial evaluated the short-term efficacy and safety of IDX899 in three groups of HIV-positive patients new to antiretroviral (ARV) treatment. The first group consisted of eight patients treated with seven days of once-daily IDX899 at a dose of 800 mg, compared with two patients who received seven days of a matching placebo. In the second group were eight patients treated with 400 mg IDX899 once daily, compared with another two placebo recipients. The third group took IDX899 200 mg/day or a placebo.
Based on the antiviral activity of IDX899 to date, the study was recently amended to evaluate a lower dose of 100 mg taken once a day.
Patients receiving once-daily 800 mg, 400 mg and 200 mg IDX899 achieved average viral load reductions of 1.78, 1.78 and 1.83 log copies, respectively, after seven days of treatment. Patients receiving a placebo saw an average viral load increase of 0.05 log copies.
CD4 counts increased during the seven-day follow-up period by at least 60 cells in each of the 800 mg, 400 mg and 200 mg dosing groups. Among the placebo recipients, there was an 80-cell decrease after seven days in the study.
Zala reported that IDX899 side effects were generally mild and similar to those seen in the placebo-treated patients. There were no severe side effects, nor were than any early discontinuations from the study due to side effects.
