MONDAY, Feb. 28 (HealthDay News) -- A new study estimates that between 10 percent and 15 percent of HIV patients in Europe and the United States are infected with a form of HIV that already has at least one drug-resistant mutation.

The researchers found that the risk of treatment failure in these patients is three times higher than normal, and said their findings confirm the need for drug resistance testing in new patients to determine which antiretroviral drugs are most likely to be successful.

For the study, 10,056 HIV patients who were beginning combination antiretroviral therapy (cART) for the first time were categorized into three resistance categories: 90.5 percent (9,102 patients) had no transmitted drug-resistance (TDR); 4.7 percent (475 patients) had at least one mutation and were receiving fully active cART; 4.8 percent (479 patients) had at least one mutation and were resistant to at least one prescribed drug.

Compared to patients without TDR, those with TDR and resistance to at least one prescribed drug were more than three times as likely to experience treatment failure, confirming "the need for at least three fully active antiretroviral drugs to optimize the virological response to a first-line regimen," the researchers wrote.

But the risk of treatment failure was not significantly different between patients without TDR and those with TDR taking a fully active cART regimen containing drugs not compromised by resistance.

The researchers also found that treatment failure was higher among patients with TDR who were taking two nucleotide reverse transcriptase inhibitors (NRTIs) plus one non-nucleotide reverse transcriptase inhibitor (NNRTI) and were predicted to be on a fully active treatment, compared to patients on protease inhibitor-based regimens whose risk of treatment failure was similar to patients with no TDR.

"If drug-resistant mutations are detected before treatment initiation, a ritonavir-boosted protease inhibitor can be included in the first treatment regimen, which, because of its higher genetic barrier, could better protect from the risk of virological failure than could NNRTI," Dr. Linda Wittkop, of INSERM, University Bordeaux Segalen in Bordeaux, France, and colleagues wrote.

"These findings confirm present treatment guidelines for HIV, which state that the initial treatment choice should be based on resistance testing in treatment-naive patients," they concluded.

The study is published in the Feb. 28 online edition of The Lancet Infectious Diseases.

More information

The U.S. National Institute of Allergy and Infectious Diseases has more about HIV treatment.