Drug combination unexpectedly flops.

A combination of therapies that researchers anticipated would work well against HIV failed to stop the virus from replicating in more than half the volunteers who received it. A second combination still appears promising, although the study is incomplete.

To compare two experimental drug regimens, researchers gave three antiretroviral drugs to each of 345 volunteers who were infected with HIV. Each day, half the volunteers received one pill containing efavirenz and another containing abacavir and lamivudine. The combination of those drugs is safe and effective against HIV. The other volunteers got tenofovir instead of the efavirenz, as well as the abacavir-lamivudine pill. The researchers then monitored the concentrations of HIV panicles in volunteers' blood.

Disturbed that some volunteers didn't appear to be benefiting greatly from treatment, Joel E. Gallant of Johns Hopkins Medical Institutions in Baltimore and his colleagues decided in July to evaluate data on the 194 volunteers who had completed at least 8 weeks of treatment. The scientists found that the viral concentrations in the blood of only 51 percent of the patients receiving tenofovir had dropped enough to be considered successful, whereas the success rate for efavirenz was 95 percent. On the basis of those findings, the researchers stopped experimenting with the combination including tenofovir.

The ongoing study continues to test whether once-daily efavirenz, with abacavir and lamivudine, could replace the common twice-daily regimen. Glaxo-SmithKline, which makes abacavir and lamivudine, funded the study.--B.H.