Little evidence of transmission of virus that's resistant to newer anti-HIV drugs

Italian investigators have found evidence of the transmission of HIV that is resistant to the fusion inhibitor T-20 (enfuvirtide, Fuzeon).

However, there is at yet no evidence that virus is being transmitted that is resistant to the integrase inhibitor raltegravir (Isentress). The investigators report these findings in the February 1^st edition of the Journal of Acquired Immune Deficiency Syndromes.

HIV can become resistant to antiretroviral drugs, and this resistant virus can be transmitted. Surveillance suggests that between 6-16% of patients newly infected with HIV in Europe have contracted virus that is resistant to one or more anti-HIV drugs in the NRTI, NNRTI or protease inhibitor classes.

It is currently recommended that all patients newly diagnosed with HIV should have a test to see if they are infected with resistant virus. The results of resistance testing can help select the combination of anti-HIV drugs that are most likely to achieve long-term suppression of HIV.

Improvements in HIV treatment and care have in recent years have been accompanied by falls in rates of transmitted resistance. Important new classes of antiretrovirals have been introduced, including the fusion inhibitor T-20 and the integrase inhibitor raltegravir. The use of these drugs has largely been reserved for patients with extensive experience of antiretrovirals and resistance to drugs in the older classes.

Little is known about the prevalence of resistance to newer classes of antiretroviral drugs in patients recently infected with HIV. Therefore between 2008 and 2010 a team of investigators in Milan tested all newly diagnosed patients for resistance to NRTIs, NNRTIs, protease inhibitors, and the newer drugs T-20 and raltegravir.

A total of 79 patients were included in the study, most of who (77%) were gay men.

Overall 18% of patients had transmitted drug resistance. This included 11% who had reduced susceptibility to NNRTIs, 9% with some resistance to NRTIs, and 4% with protease inhibitor resistance.

In addition, resistance to T-20 was detected in one patient.

T-20 was approved in 2003, and the investigators note that other studies have found evidence of the transmission of strains of the virus with resistance to this drug.

Initially, many patients taking T-20 were unable to assemble a combination of drugs to suppress their viral load to undetectable levels, leading to the development of strains of virus that were resistant to T-20. However, the advent of powerful drugs with high barriers to resistance means that an undetectable viral load is now achievable by most patients, even those with extensive resistance to older drugs.

This could explain why the investigators found no evidence of the transmission of virus that was resistance to raltegravir. The investigators note, “raltegravir was approved for clinical use in Italy in late 2007, and the prevalence of patients experiencing virologic failure is still low.”