Learn About HIV Drug Resistance
Drug resistance occurs when HIV is not effectively controlled and is able to quickly makes copies of itself. You are considered to have drug resistant HIV when the virus no longer responds to the medication you are taking.
Why Your Medication Stops Working
Class Resistance
Testing for Resistance
Why Your Medication Stops Working
When HIV makes copies of itself, it can make copies that have mutations.
Mutations
happen because HIV reproduces very quickly and mistakes are made in the process. Some of the mistakes, or mutated viruses, are harmless because they are too weak to survive and/or can not reproduce. Other mutant strains can rapidly reproduce and eventually take over as the most common type of HIV in your body. Once this happens, the antiretroviral (ARV) medication you are taking will no longer be effective.
When drug resistance occurs, your
viral load
(the amount of HIV in your blood) increases and one or more of the
antiretroviral (ARV) medications in your combination will need to be changed.
A key way to prevent drug resistance is to keep the virus from making copies of itself. That is why
adherence
to a treatment regimen is so important - consistent use of
ARV medications
helps stop the virus from reproducing.
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Class Resistance
Sometimes it takes just one
mutation
for HIV to become resistant to an entire class of
antiretroviral (ARV) medications.
This is the case with
NNRTIs.
Some HIV
mutations
lead to resistance to just one medication, but other mutations can mean your strain of HIV is now resistant to an entire drug class. This is called cross-resistance because the drug resistance to one
ARV medication
produces resistance to other
ARV medications.
On the other hand, it takes more than one
mutation
for HIV to become resistant to the entire class of
protease inhibitors (PIs).
Although a single
mutation
can cause resistance to one
PI, and in some instances several
PIs, it will not necessarily become resistant to the whole class.
Some physicians recommend starting patients on a drug combination that involves
PIs
because it is more difficult for HIV to become resistant to them than NNRTIs.
NRTIs are often used as the backbone of treatment regimens and are frequently used as the basis of first-line combination therapy. Like PIs, NRTIs also have a stronger resistance profile than NNRTIs. A single mutation can lead to resistance to one or more NRTIs, but it will not necessarily rule out the entire drug class.
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Testing for Resistance
The goal of resistance testing is to detect
mutations
in a your HIV that have known impact on the activity of one - or more - of your
antiretroviral (ARV) medications that you are taking now, and also what those that might switch to in the future.
Resistance testing has become standard for any
HAART (highly active antiretroviral therapy)
regimen that fails, but is especially important if you meet one of the following criteria:
-
You have never taken
ARV medications.
Even if you have never taken
ARV medications,
the person you acquired HIV from may have and could have developed resistance to one or more
ARVs.
This resistance could have been passed on to you.
-
Your
viral load
rises while on treatment. If you are on treatment now and your
viral load
rises, your HIV might have become resistant to one or more of your medications.
-
You need to change medications. If you need to switch one or more medications and your
viral load
is more than 1000 copies/mL, a resistance test will help identify a medication that could work better for you.
-
You are pregnant or breast-feeding. If your
viral load
is
detectable
(there are copies of the virus in your blood above the level of detection), resistance testing can help identify which drugs are not working, so you can reduce the risk of passing the virus to your baby.
For more information on types of resistance tests and how they work,
click here.
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