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Drug resistance testing is used to determine whether a patient with HIV has a mutated form of the virus that does not respond to antiretroviral therapy (ART).
If an HIV-infected patient becomes resistant to a drug and continues to take the same medication, HIV is able to multiply faster because the drug cannot stop it from replicating. When the new, mutated form is favored, it is called selective pressure. If the resistant virus makes enough copies of itself, it may eventually become the dominant type of HIV in the body. Once this happens, the medication is ineffective, and the patient will be resistant to the specific medication.
The FDA has approved the drug resistance test TrueGene™. The sensitivity, specificity, and reproducibility for many other tests have not been well established. However, several tests are available, and many health insurance plans cover them. There are two main types of drug resistance tests: genotypic and phenotypic resistance tests.
Genotypic resistance testing examines the genetic structure (genotype) of a patient's HIV. A blood sample is taken from the patient, and the HIV is analyzed for the presence of specific genetic mutations that are known to cause resistance to specific drugs. For instance, researchers have determined that lamivudine (Epivir®) and emtricitabine (Emtriva®) are not effective against forms of HIV that contain the mutation "M184V" in its reverse transcriptase gene. If a patient tests positive for this mutation, it is highly likely that he or she is resistant to both drugs, and different drugs should be prescribed.
Phenotypic testing directly measures the sensitivity (phenotype) of a patient's HIV in response to specific antiretrovirals. Many experts believe that these tests are more accurate and comprehensive than genotypic tests. These tests can help a physician determine the amount or concentration of a drug that is needed to stop a specific strain of HIV from replicating in a patient.
Clinical trials are research studies that evaluate a new medical approach, device, drug, or other treatment. As a Stanford Health Care patient, you may have access to the latest, advanced clinical trials.
Open trials refer to studies currently accepting participants. Closed trials are not currently enrolling, but may open in the future.