Researchers have studied interruptions of antiviral therapy for various reasons. These treatment interruptions are usually called structured or strategic treatment interruptions (STIs), or structured intermittent therapy (SIT).
During most treatment breaks, the viral load climbs very quickly and T-cell counts drop. Some people get the same symptoms as if they were newly infected with HIV.
When people start medications again after taking a break, they might experience more side effects, like when they first started taking antiviral drugs. They might also have difficulty with adherence , taking all of their doses correctly.
There were several reasons why treatment interruptions were studied:
1. People who started treatment as soon as they got infected.
It seemed possible that antiviral medications started immediately after HIV infection could protect the immune system from damage. A break in treatment might help the immune system "recognize" the HIV infection and fight it. The hope was that in these rare cases, patients could stop taking medications.
Unfortunately, this approach now does not seem to work. There are several reasons. First, most people aren't aware that they have just been infected with HIV. Once HIV infection has continued for a few months, it's too late for this approach. Also, researchers cannot predict which patients might be able to stop their therapy. But most important, newer research shows that the immune response in these patients does not continue to protect them against HIV disease.
2. People on therapy who don't meet current treatment guidelines.
During the past few years, HIV treatment guidelines have gotten more conservative. They recommend that people start treatment with lower T-cell counts than previous guidelines.
Some people started treatment with higher T-cell counts than today's guidelines. In some cases, their doctors will recommend that they stop taking medications. They check their T-cell counts and their viral loads regularly. They go back on therapy when they meet the current guidelines.
As more doctors follow the newer guidelines and delay treatment for their patients, there won't be as many people who started treatment "too early."
3. Using "intermittent therapy" to reduce side effects and costs.
Recently, doctors have studied "cycling" people on and off of antiviral therapy. Their goal was to give patients more time off of therapy, and reduce side effects, while still controlling HIV.
Two types of "cycling" have been studied. The first type put patients on a fixed schedule. They would start and stop therapy for a certain number of days or weeks. This seems not to be very effective, because HIV doesn't stay under control for the same length of time in every patient.
The second type of cycling uses T-cell counts and/or viral loads to decide when to end a treatment break and start medications again. This approach is still being studied.
4. Stopping treatment to deal with drug side effects.
Some patients get very serious side effects. In some cases they can switch medications. However, if they have already used most antiviral drugs, they might need to take a break from treatment to recover from the side effects before getting back on treatment.
5. Waiting for a new drug to be approved.
Some doctors used to stop treatment for their patients when there wasn't any treatment regimen that could control their virus. Maybe HIV had developed resistance to all of the available drugs.
During a treatment interruption, the "wild type" virus becomes more common. At first, researchers thought this was a good thing, because the wild type virus can be controlled by medications. However, most viral resistance doesn't go away. It can come back quickly when drugs are re-started. Most patients do better if they keep taking medications, even if HIV is not totally controlled.
Doctors and patients should plan treatment interruptions. Viral load and T-cell levels should be carefully monitored. Just skipping doses is risky and does not contribute to knowledge about HIV treatments. Medications to prevent or treat opportunistic infections should not be interrupted.
WHAT ARE THE RISKS?
The biggest risks of an STI are that the viral load will climb and the T-cell count will drop. These risks are greatest for people whose virus is not under control or who have a low T-cell count. If you have only 50 T-cells, losing another 10 might have serious consequences. Stopping medications to prevent opportunistic infections can allow them to develop. A research study on STIs showed that people who stopped treatment had a much higher chance of developing an opportunistic infection.
Stopping and re-starting medications could make it easier for the virus to develop resistance to medications. This has happened to some patients in STI studies.
People ending a treatment interruption might have a hard time re-starting medications. This can be due to side effects, or due to psychological difficulties in getting back on treatment.
THE BOTTOM LINE
HIV patients stop antiviral treatments for various reasons. If we can learn how to use treatment interruptions safely, patients might be able to take periods of time off of antiviral drugs. This could mean fewer side effects and lower drug costs. However, we will have to learn how to minimize drug resistance and transmission of HIV, and learn the best scheduling of treatment interruptions to avoid long term increases in viral load and decreases in T-cells.
AIDS Factsheet 
