Resistance to HIV Medicines
The 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 immune system.
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 their worst.
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:
Two tests are available to detect resistance to medicines used to treat HIV infections:
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:
If resistance has occurred, your doctor may need to change your antiretroviral medicines.
eMedicineHealth Medical Reference from Healthwise
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