How Can Drug Resistance Be Measured?
Over the past five years, a significant number of breakthroughs have been made in understanding the power of antiretroviral drugs against HIV. With the development and availability of viral load tests — such as PCR, bDNA, and NASBA — we can determine from a blood sample how much virus is replicating in the body. If viral load increases substantially while a person is on a combination of antiretroviral drugs, the most likely culprit is drug resistance. Unfortunately, viral load tests cannot determine whether or not HIV is resistant to one drug in particular or the entire combination. Moreover, in a person with drug-resistant HIV, these tests cannot determine which drug or combination of drugs is likely to be the most effective in the future. Two general approaches are now used for measuring resistance to HIV drugs. The first is called genotypic testing. Genotypic tests can help determine whether specific genetic mutations are causing drug resistance and drug failure. The second method
