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HIV and AIDS Current Topics in HIV and AIDS

The Fight Against HIV: Resistance Testing

Since the first case of AIDS was reported in 1981, researchers have been trying to develop treatments to help keep the HIV virus at bay. One of the newest techniques, resistance testing, may help to increase success rates even more.

To date, the most effective treatment for HIV is highly active antiretroviral therapy, more commonly known as HAART. This combination of medications is used to fight the various forms of HIV that may be present in your body. When taken regularly, HAART lowers the amount of virus to a level where it can no longer attack your body in a significant way.

Astoundingly, up to 10 billion new HIV viruses are produced daily inside an infected person. Of these, 10 million will be produced that have a mutation, or error, in their genetic code. While most of these errors will be fatal to the virus, a few resistant forms may be created which can outmaneuver traditional HAART treatment.

Traditionally, resistance is detected indirectly: If the amount of HIV in the blood fails to drop after beginning HAART, doctors may switch to other drug combinations to try to keep the virus in check. Finding resistance before treatment even begins, however, can help speed treatment, lower drug costs and prevent damage to the body.

That's where HIV resistance testing comes in. This test provides doctors and patients a picture of the mixture of HIV mutations present in a patient's body.

"There is an advantage of doing drug resistance testing as soon as possible," says Rowena Johnston, PhD, director of basic research at The American Foundation for AIDS Research (amfAR). "It will inform treatment decisions, even if those decisions don't come until years and years down the line."

There are two types of resistance testing:

• Phenotypic resistance—A sample of the HIV virus is grown in a lab and then mixed with various antiviral drugs. If some of the virus continues to grow, resistance has been determined. Then, the types and concentrations of the medication can be altered until the virus is fully under control in the test tube.
• Genotypic resistance—A lab technician will look directly at the genes of the HIV virus, looking for mutations in the region where the antiviral drugs work. Particular mutations have been linked to a particular drug resistance.

If you are newly diagnosed with HIV, Johnston recommends that you have a genotypic resistance test done first. Early in the course of the disease, the mutant viruses will be more easily detectable than later, making it much easier for doctors to spot potentially resistant strains.

If you have had HIV for several years and are about to start treatment or are currently going through treatment, phenotypic testing is probably better, according to Johnston. Even though it takes longer and is more costly, this test is much better at finding the small number of viruses that may be resistant to the drugs you are taking.

If you know that you have HIV, consider speaking with your doctor about the availability of resistance testing in your area. A simple blood test gives your doctor an edge once treatment begins. Then again, if you are unsure of your HIV status, be sure to get tested. There are many clinics nation-wide that offer free, confidential testing. After all, "there is nothing to lose and everything to gain," says Johnston.