Use of HIV resistance testing after prolonged treatment interruption.

Background: HIV-1 genotypic resistance testing is not routinely recommended for patients who have been off antiretroviral therapy (ART) for longer than 4 weeks. We assessed the results and use of resistance testing in patients off ART. Methods: All HIV resistance genotypes from November 2003 through April 2008 were reviewed from one large teaching hospital and two private HIV practices. Inclusion criterion was having a genotypic resistance test after an ART interruption of at least 2 months. Medical records were reviewed using a standardized data collection sheet. Results: Sixty-two of 304 treatment-experienced patients with HIV genotypes met the inclusion criteria. Prior cumulative ART class exposure included nucleoside reverse transcriptase inhibitors in 54 patients, nonnucleoside reverse transcriptase inhibitors in 32 patients, and protease inhibitors in 30 patients. Resistance testing was performed at a mean of 12 months (range, 2.5-48 months) after ART interruption. The mean time between ART interruption and resistance testing did not differ for patients with mutations and those without mutations detected. Seventeen of 62 (27.4%) patients were found to have resistance mutations. Eleven patients were found to have mutations to nonnucleoside reverse transcriptase inhibitors, four patients had mutations to nucleoside reverse transcriptase inhibitors, and two patients had protease inhibitor-associated mutations. No patient had multiclass resistance. Among the 17 patients with mutations after treatment interruption, 15 had mutations that were either not present on a prior genotype (n = 2) or did not have a prior genotype (n = 13). Conclusions: HIV genotypic resistance assays may identify mutations even when performed after a prolonged treatment interruption and may offer clinically significant information. Current guidelines that discourage resistance testing after treatment interruptions of longer than 4 weeks should be re-evaluated.