human immunodeficiency virus (HIV) changes (mutates)
often. Sometimes these changes make the virus resistant to a particular
medicine or class of medicines, which means the medicine is no longer effective
against the virus. When this happens, the medicine no longer controls virus
growth (replication) or protects the
Resistance testing is done to determine whether
resistance has caused treatment to fail and to identify antiretroviral
medicines that can be used to treat the infection. There are many reasons that
treatment fails, such as:
It is possible that the main title of the report AIDS (Acquired Immune Deficiency Syndrome) is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.
The virus is initially resistant to one or more antiretroviral
medicines, or the virus mutates and stops responding to the
There is a change in the way your body absorbs a
There are interactions between two or more medicines that
you are taking.
You have not taken your medicine as
Two tests are available to detect resistance to medicines
used to treat HIV infections:
Genotyping assays detect
medicine resistance mutations in the viral genes. It takes 1 to 2 weeks to get
Phenotyping assays measure the
ability of viruses to grow in cells with various concentrations of
antiretroviral medicines. It takes 2 to 3 weeks to get the results.
Both of these tests are done on a sample of blood taken from
a vein. These tests may not be accurate if the resistant virus is less than 20%
of the circulating virus.
You may be tested for infection with a
resistant virus when:
You are diagnosed with an HIV infection.
Your viral load has not decreased by at least one-half after 4
weeks of therapy.
Your viral load has not decreased to a
undetectable level within 4 to 6 months of beginning treatment. An undetectable
level is defined as less than 50 copies/mL.
Your viral load is detectable after having been at an
Resistance reduces the number of treatment options in the future, so it is important to keep resistance from happening.
In this article
This information is produced and provided by the National
Institute (NCI). The information in this topic may have changed since it was written. For the most current information, contact the National
Institute via the Internet web site at http://
.gov or call 1-800-4-CANCER.
WebMD Medical Reference from Healthwise
April 05, 2012
This information is not intended to replace the advice of a doctor.
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