Test pegs resistance after single-dose nevirapine.(News)

BOSTON -- Early findings from a test for detecting the most common HIV mutation suggest that the number of women who develop resistance to the anti-HIV drug nevirapine after receiving a single intrapartum dose has been substantially underestimated, according to the Centers for Disease Control and Prevention.

Using a new method called real-time polymerase chain reaction (RT-PCR), investigators have been able to detect the prevalence of the K103N mutation down to 0.1%--about 100 times more sensitive than standard assays, reported Jeffrey Johnson, M.D., of the CDC in Atlanta.

The K103N mutation causes high-level resistance to nevirapine as well as cross-resistance to other nonnucleoside reverse transcriptase inhibitors, including efavirenz and delavirdine, he said at a conference on retroviruses and opportunistic infections.

Dr. Johnson and colleagues employed the assay to analyze blood samples collected before drug treatment and between 6 and 36 weeks post partum from 50 HIV-positive women in South Africa who received single-dose nevirapine during labor. They also applied the test to 10 control samples that had tested positive for resistance by conventional assay and to a representative sample of 40 specimens that tested negative initially.

None of the pre-nevirapine samples had detectable levels of the viral mutation using the new assay, and the 10 samples that tested positive for the mutation via conventional methods also tested positive with the more sensitive test, Dr. Johnson said at the conference sponsored by the Foundation for Retrovirology and Human Health.

Among the 40 posttreatment samples that tested negative with standard testing, 17 tested positive for the mutation using the new assay, increasing the total incidence of resistance 63%. "With the highly sensitive test, 65% of the women had evidence of the mutation," Dr. Johnson ...