US regulators have put a stop to a major international trial investigating a new regime of antiretroviral therapy (ART) for HIV patients, as it was revealed that thousands of participants were in danger of actually becoming sicker.

The SMART trial (Strategies for Management of Anti-Retroviral Therapy) had enrolled 5,472 patients across 33 countries, and was designed to assess on-off ART, which involves administering drugs only when patients’ immune systems are showing signs of weakening, in the hope that both side-effects and costs would be reduced.

But the US National Institute of Health halted the study after it came to light that patients were twice as likely to become ill, or die, than those taking treatment every day.

Furthermore, a review by an independent Data and Safety Monitoring Board found a rise in complications, including cardiovascular, kidney and liver diseases, diarrhoea and drug resistance, in patients on stop-start therapy. Although such effects are normally associated with ART, it was hoped that they would be seen less frequently in patients taking less medicine.

Commenting on the findings, Wafaa El-Sadr of the Harlem Hospital Center and Columbia University in New York City, a principal investigator of the trial, said: “We were surprised to learn that in the short term, episodic antiretroviral therapy carries such an increased risk without evidence of sparing patients the known side effects associated with ART.”

But James Neaton, PhD, of the University of Minnesota and another principal investigator for the study, pointed out that “The SMART trial reached a conclusion much earlier than we expected. That is the significant value and potential power of conducting such a large trial.”