Page 29 - HIV/AIDS Guidelines

Resistance testing also can help guide treatment decisions for patients with suboptimal viral load reduction
(AII). Virologic failure in the setting of combination ART is, for certain patients, associated with resistance
to only one component of the regimen. 44-46 In that situation, substituting individual drugs in a failing regimen
might be possible, although this concept will require clinical validation. (See Virologic and Immunologic
Failure.)
Genotypic testing is generally preferred for virologic failure or suboptimal viral load reduction in persons
failing their first or second ARV drug regimen because of lower cost, faster turnaround time, and greater
sensitivity for detecting mixtures of wild-type and resistant virus (AIII). Addition of phenotypic to genotypic
testing is generally preferred for persons with known or suspected complex drug-resistance mutation
patterns, particularly to PIs (BIII).

In patients failing INSTI-based regimens, testing for INSTI resistance should be considered to determine
whether to include drugs from this class in subsequent regimens; genotypic testing is preferred (BIII).
Although it is not a drug-resistance assay, a coreceptor tropism assay should be performed whenever the use
of a CCR5 antagonist is being considered (AI). Coreceptor tropism testing should also be considered for
patients who exhibit virologic failure on a CCR5 antagonist (CIII). However, such testing may be of limited
value because the absence of detectable CXCR4-using virus does not exclude the possibility that CCR5
antagonist resistance may have developed. Assays for detecting resistance to CCR5 antagonists are not yet
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commercially available. (See Coreceptor Tropism Assays.)
Use of Resistance Assays in Pregnant Women
In pregnant women, the goal of ART is to maximally reduce plasma HIV RNA to provide appropriate
maternal therapy and prevent mother-to-child transmission (MTCT) of HIV. Genotypic resistance testing is
recommended for all pregnant women prior to initiation of therapy (AIII) and for those entering pregnancy
with detectable HIV RNA levels while on therapy (AI). Phenotypic testing may provide additional
information in those found to have complex drug-resistance mutation patterns, particularly to PIs (BIII).
Optimal prevention of perinatal transmission may require initiation of ART while results of resistance testing
are pending. Once the results are available, the ARV regimen can be changed as needed.

Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents C-11

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