And That's Not All, Folks
March 31 2004 1:00 AM ET
What exactly happens when a virus becomes drug-resistant, and what can you do about it? Making billions of copies of itself a day, HIV will occasionally create an imperfect, or mutant, copy of itself. This new version of the virus may be resistant to antiretroviral medications, meaning that the drugs are not able to effectively fight the virus anymore. Consequently, since your medications do not kill this one copy, it multiplies until it becomes a more dominant presence in the blood stream than that of the original, or 'wild-type' virus. (This is most likely to happen if you have missed doses of your meds.) Complicating the matter further, you may also develop 'cross resistance' to medications that are in a similar class to those you are currently taking.
Fortunately, in the face of such a dose of bad news, there is an arsenal with which to fight back. First of all, drug-resistance tests can help you decide which medications are more likely to work for you. And second, even if you are resistant to all medications, researchers say you should stay on highly active antirotroviral therapy, since your drugs are still fighting the wild-type virus in your body [see accompanying article 'Do Not Quit Yet'].
How Fit Is It?
If genetic testing or treatment failure suggest you have a drug-resistant strain of HIV, there is a silver lining: Mutated viruses are less 'fit,' meaning they replicate more slowly than the nonresistant, or 'wild type' virus. To give you an idea of how fit your virus is, there is a new lab test called a viral replication capacity test, which you can request along with HIV drug resistance phenotype testing.
By comparing the performance of your virus in a test tube to that of a wild-type virus, lab technicians can assess your replication capacity. Your test result is presented as a percentage'anything above 100% is a more fit virus than the wild type and anything lower is less fit. However, according to Sidney Ho, a spokesman for ViroLogic, which manufactures the test, the precise significance of one percentage over another is still not clear; more research needs to be done on the matter.
If your strain of HIV does have a low replication capacity, you may be able to maintain both a high viral load and a stable CD4 count. This seeming contradiction happens because the immune system is able to keep up with a virus that replicates slowly. You and your physician may be able to use your test results to make treatment decisions for you based upon this phenomenon.