WEDNESDAY, Sept. 12, 2012 (HealthDay News) -- Truvada, the only medication approved by the U.S. Food and Drug Administration for HIV prevention, is effective in blocking the virus even if people do not adhere to their daily regimen perfectly, a new study indicates.
The researchers say their findings build on a 2010 clinical study, called the iPrEx study, which found Truvada could prevent new infections in people at high risk for HIV.
"After the initial iPrEx study, there was concern that the protective effect of Truvada was fragile, and that individuals taking the drug would need to adhere perfectly to daily regimen for it to work," study co-leader Dr. Robert Grant, an investigator at Gladstone Institutes and professor at the University of California, San Francisco, said in an institute news release. "This new study suggests that Truvada can help block the virus even if the person on a daily regimen doesn't always adhere perfectly."
To determine the effectiveness of Truvada if people didn't take the medication exactly as prescribed, the researchers developed a clinical trial in which two, four or seven doses per week of the drug were given to 24 people who were not infected with HIV.
The investigators measured the different concentrations of the drug in the participants' blood and compared these concentrations to those of participants in the iPrEx study. The researchers used the comparison to determine how well the people involved in the first study adhered to their drug regimen and how well their concentration of the drug was able to protect them against HIV.
"Surprisingly, we found that the iPrEx participants didn't have to adhere perfectly to the drug regimen to reap Truvada's benefits," said Grant. "Even in those patients who didn't adhere perfectly, their risk of contracting HIV still dropped by more than 90 percent -- offering a high level of protection against the virus."
The researchers concluded that their findings help determine the most effective dose of the drug, which would reduce costs and increase convenience for patients.
Study co-leader Peter Anderson, from the University of Colorado, explained that the researchers' next step "is to take the methods we've developed and create simple yet powerful tools that can measure drug adherence to help doctors monitor how well Truvada is working in their patients. Yet until these and other efficacy studies of alternative dosing strategies have been completed, the only regimen that that should be used in clinical practice is the FDA-approved one Truvada each day."
Grant added: "Patients should still take one pill a day to achieve the best results, and we encourage people to explore multiple methods to prevent HIV -- such as regular condom use, early treatment of HIV infection in partners, good communication and male circumcision. We hope that our findings lead to more effective use of prevention tools that finally squash the HIV/AIDS epidemic."
The study was published online Sept. 12 in the journal Science Translational Medicine.
The U.S. National Institute of Allergy and Infectious Diseases has more on HIV treatment.