When Should I Change My Treatments, and Which Drugs Should I Switch To? en español
What if my virus has become resistant to the drugs I'm taking?
We've come a long way in terms of managing virus that has become resistant to anti-HIV drugs. In the past, if your viral load became detectable while taking a combination of three drugs, the general advice was to stop the three drugs and switch to a batch of three different drugs. Research studies have demonstrated that, when a combination of drugs is unable to keep viral load undetectable, it is usually because the virus has become partially or fully resistant to one or two drugs – not the entire regimen.
Now that drug-resistance testing is widely available, doctors are better equipped to deal with drug-resistant HIV. For example, let's say you are taking a drug combination consisting of Sustiva® (efavirenz) and Combivir® (zidovudine/lamivudine). Your viral load goes undetectable. Approximately a year later, you see your viral load increase to 5,000 – a sign that your drug combination is no longer working correctly. After a drug-resistance test is performed, it is determined that your virus is still sensitive to the Combivir, but has become resistant to Sustiva. With this information, you and your doctor may simply want to stop the Sustiva – perhaps switching it for a protease inhibitor – and keep the Combivir. In other words, drug-resistance testing can help you save the drugs that are working for you while helping you find new options for those drugs that aren't working for you.
Sometimes, it's not necessary to switch any medications. An option that is becoming increasingly popular is to add new medications to an existing regimen. For example, let's say you are taking a regimen consisting of Lexiva® (fosamprenavir) and Truvada® (tenofovir/emtricitabine). After several months of your virus being undetectable while taking this regimen, your viral load rises to 5,000 and a drug-resistance test determines that your virus has become partly resistant to the Lexiva. One option might be to switch the Lexiva for another protease inhibitor. But this might not be effective, because if your virus becomes resistant to one protease inhibitor, it may be less sensitive to other protease inhibitors as well (this is called "cross resistance"). Another option is to add the protease inhibitor Norvir® (ritonavir) to your regimen. This is because Norvir can increase the amount of Lexiva in the bloodstream, thereby making the drug much more effective against the virus, even if it has started to become resistant to the drug. When Norvir is added, a low dose of the drug is used and the dose of Lexiva is reduced.
Another example: Let's say your virus has become resistant to the emtricitabine in Truvada. Instead of dropping the Truvada, your doctor may want to add Retrovir® (zidovudine), another nucleoside analogue. The reason for this is that the mutation (change) in HIV's structure that causes resistant to emtricitabine actually makes the virus more sensitive to Retrovir. In turn, adding Retrovir may improve the potency of the regimen and help bring viral load back down to undetectable levels.
Of course, dropping drugs – and, sometimes, an entire regimen – in order to switch to new drugs is still necessary for a lot of HIV-positive people in order to keep viral load low and CD4 cells high. To help maximize the effectiveness of switching drugs, drug-resistance testing has proved to be extremely useful.
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