Skip to content
My WebMD Sign In, Sign Up

HIV & AIDS Health Center

Font Size

Resistance to HIV Medicines - Topic Overview

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.

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:

Recommended Related to HIV/AIDS

The Top 10 Myths and Misconceptions About HIV and AIDS

For nearly 30 years, HIV (human immunodeficiency virus) and AIDS (acquired immunodeficiency syndrome) have been shrouded in myths and misconceptions. In some cases, these mistaken ideas have prompted the very behaviors that cause more people to become HIV-positive. Although unanswered questions about HIV remain, researchers have learned a great deal. Here are the top ten myths about HIV, along with the facts to dispute them.

Read the The Top 10 Myths and Misconceptions About HIV and AIDS article > >

  • The virus is initially resistant to one or more antiretroviral medicines, or the virus mutates and stops responding to the medicines.
  • There is a change in the way your body absorbs a medicine.
  • There are interactions between two or more medicines that you are taking.
  • You have not taken your medicine as prescribed.

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 the results.
  • 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 undetectable level.

Resistance reduces the number of treatment options in the future, so it is important to keep resistance from happening.

1

WebMD Medical Reference from Healthwise

Last Updated: April 05, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
Next Article:

Resistance to HIV Medicines Topics

Today on WebMD

misconception
How much do you know?
contemplative man
What to do now.
 
research
Should you be tested?
HIV under microscope
What does it mean?
 
HIV AIDS Screening
Slideshow
man opening condom wrapper
Quiz
 
HIV AIDS Treatment
Feature
Discrimination Stigma
Feature
 
Treatment Side Effects
Feature
grilled chicken and vegetables
Article
 
obese man standing on scale
Article
cold sore
Article
 

WebMD Special Sections