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
If you start taking
antiretroviral medicines early in the course of your infection, before your
CD4+ cell counts have dropped and before your
viral load has increased, you may "cycle through" all
the available medicines. In this case, you may exhaust all the available
medicines and have no options left when your viral load and CD4+ counts are at
Lipodystrophy is a problem with the way the body produces, uses, and stores fat. It is also called fat redistribution. Since the widespread use of antiretroviral therapy began, the numbers of HIV-positive people with lipodystrophy has increased. Today, lipodystrophy occurs in 30% to 50% of people who are infected with HIV (human immunodeficiency virus).
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:
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 (by bDNA or RT-PCR test
Your viral load is detectable after having been at an
If resistance has occurred, your doctor may need to change
your antiretroviral medicines.