Structured treatment interruptions (STIs), also called structured intermittent therapy (SIT) or drug holiday, describes scheduled breaks in drug regimens for HIV.
Researchers began studying treatment interruptions after it was reported that a handful of HIV patients were able to maintain a very low number of viral particles in the blood (viral load) when they took a break from treatment. It was suggested that STIs might offer benefits for HIV patients, including reduced cost and side effects.
However, large-scale studies have not found any benefit in stopping treatment. In fact, research suggests that stopping and starting treatment can have serious negative effects on an HIV patient. STIs may increase the rate of disease progression to AIDS (acquired immune deficiency syndrome) and may lead to an increased risk of infection and drug resistance. Once a patient becomes resistant to a drug, that particular medication is no longer effective, even if it is taken in the future.
It is possible that future studies may find benefit for treatment interruptions in specific subgroups of HIV patients, such as children.
Patients should not discontinue or alter their medications without first consulting their healthcare providers.
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General: Two types of cycling have been studied. The first type of cycling was based on the patients' CD4 cells counts and/or viral loads. When levels were adequate, therapy was stopped and when CD4 counts decreased and HIV loads increased, patients were restarted on therapy. The second study was based on a fixed schedule. Patients stopped and started treatment after a certain number of days. Both studies compared intermittent drug therapy with continuous therapy.
Strategies for the Management of Antiretroviral Therapy (SMART) trial: Researchers of the Strategies for the Management of Antiretroviral Therapy (SMART) trial set out to determine whether antiretroviral therapy (ART) could be used only when needed, instead of continuously. Before the study began, it had been suggested that patients who began ART soon after diagnosis were able to safely interrupt treatment.
The study, which began in 2002, included 5,472 participants from 33 countries making it the largest treatment strategy trial ever conducted. Participants received ART when their CD4 counts dropped below 250 cells per microliter of blood. Treatment was stopped when their cell count increased to 350 CD4 cells per microliter of blood.
In January 2006, SMART's Data and Safety Monitoring Board (DSMB) recommended that the trial end early because nearly twice the number of the participants in the intermittent therapy group progressed to AIDS, compared to the group receiving continuous therapy. Also, several participants in the intermittent therapy group died, and many others experienced serious complications associated with drug toxicity. Investigators of the study agreed with the DSMB and advised all participants to restart ART.
Development of Anti-Retroviral Therapy in Africa (DART): Soon after the SMART study ended, the treatment interruption group of another study titled, Development of Anti-Retroviral Therapy in Africa (DART), also ended early. In this study, patients who had a CD4 cell count of 300 or higher were randomized to receive either continuous ART or 12-week cycles of antiretrovirals, followed by a 12-week break.
However, researchers of the DART study noted similar results to the SMART study. According to the researchers, patients who received intermittent ART were more likely to develop HIV-related illnesses and AIDS-defining illnesses than patients who received continuous therapy. Patients in the treatment interruption group were advised to restart continuous ART. The researchers concluded that 12-week cycles of antiretroviral therapy, followed by 12-week breaks in treatment, were unsafe for patients who started treatment with a CD4 cell count lower than 200 cells per microliter of blood or for patients with a history of HIV-related illnesses.