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resistance
Oct 29, 2005

what is resistance

Response from Dr. Sherer

This is an important question for anyone with HIV infection to understand.

Resistance to antiretroviral therapy (ART) refers to genetic changes in an individual person's dominant strain of HIV that enable the virus to continue to replicate and spread in the presence of ART.

Resistance is most commonly recognized when a patient has a positive response to ART - with suppression of viral replication below levels of detection and rising CD4 cells - that is then followed by plasma viremia, i.e. repeatedly detectable levels of viral RNA in the blood. When resistance tests are performed in this setting while the patient is still taking the initial ART regimen, new genetic mutations are seen that are associated with partial or complete loss of susceptibility to one or more of the drugs in the ART regimen.

Unfortunately, we are also seeing patients who have never been treated with ART who have some resistance due to the transmission of HIV strains that have resistance mutations. For this reason, in areas of a prevalence of resistance mutations in new HIV infections of 5% or greater, current ART treatment guidelines advise that physicians should obtain a resistance test before starting the first regimen, in order to detect resistance mutations and to select ART to which the patient's virus will be fully susceptible.

Unfortunately, resistance is very common in patients who have been treated with ART for a year or more. Factors that have been linked to an increased risk of resistance include more advanced disease when ART is started, i.e. low CD4 cell counts (less than 50, or less than 200), and high viral loads (greater than 100,000 copies/ml).

Probably the most important variable that increases the risk of resistance that is within a patient's control is adherence to ART. Resistance becomes more likely when patients are irregular with their medication schedule, particularly if they miss doses or are often very late with their doses.

We describe HIV infection as 'unforgiving'. Once resistance mutations have occured, they are permanent, and they may compromise the effectiveness of an ART regimen now or in future. For this reason, HIV physicians and clinicians devote much time and energy to trying to ensure the best possible adherence to ART, so that the risk of resistance is mitigated to the greatest extent possible.

I urge anyone with HIV to talk to their doctor about resistance, and to learn what steps they can take to prevent it.


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