Given in combination with reverse transcriptase inhibitors, they can reduce the virus in the blood to undetectable levels in many patients, at least for a period of time. However, the fact that the virus can't be detected doesn't mean that it has been eliminated. While antiretroviral drugs may control HIV infection, they do not provide a cure. If therapy is stopped or interrupted, most researchers believe the virus is likely to reappear. When an antiretroviral drug begins to lose its effect, it is usually because the virus has developed resistance to the drug.
Resistance occurs when certain mutations in the virus make it less sensitive to a drug.
HIV is particularly good at developing drug-resistant mutations. This is a major reason why the virus has been so difficult to eliminate. Drug resistance can develop to any antiretroviral drug, especially when the drug is given alone instead of combined with other antiretrovirals. Resistance also occurs more frequently when a drug is not consistently taken according to the treatment schedule. You need to know exactly what's going on with your drugs, especially how to take them.