Treatment failure was significantly more common among patients with transmitted drug resistance, despite the use of genotype results to select drugs that appeared to be fully active. Reasons for this finding are not obvious. Given that PIs were used more often in those with TDRM, one could conclude that non–PI-based therapy has superior efficacy, but available clinical trial results suggest otherwise. An alternative explanation is that commercially available resistance testing does not reliably detect the presence of mutations expressed in low frequency, and that such mutations occur more commonly in those with any detectable resistance. Thus, the presence of detectable TDRM may be a proxy for more-widespread resistance than is apparent on the test results. Clinicians must remember that resistance test results are most helpful in determining which drugs not to use — and should remain vigilant for treatment failure, even when the regimen appears to be fully active based on resistance testing.
AIDS Clinical Care © 2012 Massachusetts Medical Society