By Liz Highleyman

Resistance to antiretroviral therapy is mainly seen in treatment-experienced patients exposed to these drugs, but there is increasing evidence that resistant HIV can be transmitted to newly infected individuals, a phenomenon known as primary drug resistance.

To learn more about the prevalence of primary drug resistance, researchers used genotypic testing to measure resistance in a group of 103 previously untreated subjects with unknown duration of HIV infection. Results were reported in the February 1, 2007 issue of Clinical Infectious Diseases.

Results

• 26 treatment-naive study participants (25%) had resistance to at least 1 class of antiretroviral drugs.

• 6% had resistance to 2 drug classes, while 1% were resistant to all 3 major classes (protease inhibitors [PIs], non-nucleoside reverse transcriptase inhibitors [NNRTIs], and nucleoside/nucleotide reverse transcriptase inhibitors [NRTIs]).

• The most common resistance mutation overall (detected in 12 patients) was K103N, which confers resistance to NNRTIs.

• The M184V mutation, which confers resistance to certain NRTIs, was detected in 6 patients.

• 2 patients had PI-resistance mutations.

Conclusion

"In clinical settings, we have found a high rate of HIV drug resistance among antiretroviral-naive patients for whom the duration of infection was unknown," the investigators concluded. "These high rates were most likely the result of both transmitted resistance and informal antiretroviral use, and they suggest that routine resistance testing among antiretroviral-naive patients would be a cost-effective clinical practice."

The resistance rate observed in this study (done in 2005) was higher than the rates seen in previous studies -- ranging from 8% to 20% -- suggesting that the prevalence of primary drug resistance may be increasing over time.

Current International AIDS Society guidelines recommend that individuals known to have been infected within the previous year should undergo resistance testing before starting antiretroviral therapy. The present results, however, suggest that resistance testing should be performed for all patients starting therapy, since most are not diagnosed within the first year after infection or do not know their date of infection.

02/02/07

Reference
D Smith, N Moini, R Pesano, and others. Clinical utility of HIV standard genotyping among antiretroviral-naive individuals with unknown duration of infection. Clinical Infectious Diseases 44(3): 456-458. February 1, 2007.