Nevirapine, an anti-AIDS drug widely used to prevent mother-to-child transmission, may substantially raise drug-resistance of the HIV virus, according to three new studies released on Wednesday.

A single dose of nevirapine given to an HIV-infected pregnant woman during delivery, and another given to her newborn, can cut the mother-to-child HIV transmission rate by half. The simplicity and affordability of single-dose nevirapine make it the drug of choice for prevention of mother-to-child transmission in many developing countries.

The new researches expand understanding of the risks of drug resistance associated with nevirapine, but the clinical implications for patients are not yet clear, noted research groups in the July 1 issue of The Journal of Infectious Diseases.

More research is necessary to determine whether nevirapine used to prevent mother-to-child transmission affects the chances of successful treatment later with similar drugs, scientists said.

Two of the studies analyzed the incidence of nevirapine- associated resistance using laboratory tests more sensitive than standard genotypic assays.

In the first, researchers of US Centers for Disease Control and Prevention (CDC) used a very sensitive technique to detect resistance mutations in samples of HIV-1 obtained from 50 South African women before and after treatment with single-dose nevirapine.

Previously, the researchers had used a less-sensitive conventional technique to estimate that viral resistance to nevirapine emerged in approximately 40 percent of women after receiving the single-dose therapy.

But the CDC group concluded that resistance emerges in at least 65 percent of women after use of single-dose nevirapine. This finding indicates that more than one-third of the resistance that emerges from this intervention is undetected by conventional laboratory tests.

In the second study, researchers from Johns Hopkins University analyzed HIV samples from nine mothers and five infants in Uganda who had received single-dose nevirapine. The researchers used standard sequencing techniques and, like the first group of researchers, two more-sensitive assays.

The more-sensitive assays detected resistance mutations a year or more after use of single-dose nevirapine, whereas the conventional assay could not detect resistance at one or two years.

Taken together, these two studies indicate that resistance after the single-dose therapy occurs more frequently and may persist longer in the circulation than previously thought.

The third study asked whether the rate of nevirapine resistance differs according to HIV-1 subtype. The researchers examined the rate of nevirapine resistance after single-dose therapy in 65 women in Malawi infected with subtype C, the most common subtype in many developing countries where single-dose nevirapine is used, as compared with that of 241 women in Uganda infected with subtypes A or D.

The frequency of mutations linked with nevirapine was significantly higher in women with subtype C virus (69 percent) than in those with subtype A (19 percent) or subtype D (36 percent) , the researchers found.

An editorial in the journal emphasized that these studies raise questions for additional research, including whether the presence of nevirapine-linked resistance mutations in women and children compromises the subsequent treatment of their HIV infection.

An alternative approach to single-dose nevirapine, combination therapies, can reduce rates of newborn HIV infection while reducing the risk of resistance in the mother. But it is more expensive and may require more health care infrastructure, the editorial noted.

Source: Xinhua