What are the aims of iPrEx OLE?

iPrEx OLE is gathering additional information about the use of Truvada PrEP, including information on:

• Long-term efficacy
• Long-term safety
• Pill taking and adherence
• Any changes in participants’ sexual behavior
• Drug resistance
• Bone mineral density and fat distribution
• Impact on hepatitis infection


iPrEx demonstrated that PrEP with Truvada is safe and well tolerated.  Extensive studies have demonstrated the safety of Truvada in people living with HIV, but iPrEx is the first study to show that the drug is safe and well-tolerated in people who are HIV-negative.  There was no difference in moderate and severe adverse events between participants who received Truvada and those who received a placebo in the first phase of the iPrEx study. iPrEx OLE continues clinical observation and laboratory testing to measure the safety and tolerability of Truvada among study participants.
More information about the safety findings from the iPrEx study is available here. 

Pill-taking and Adherence

PrEP must be taken consistently to work. A number of research studies have demonstrated, however, that taking a daily pill can be challenging for many people.

iPrEx OLE continues the study’s evaluation of a number of methods designed to help encourage people in the study to take the study medication consistently.  We also hope to determine whether the knowledge that PrEP provides some protection against HIV infection, and the fact that everyone who wants to participate in the drug portion of iPrEx OLE will receive Truvada (no placebo is used in iPrEx OLE), will help participants achieve more consistent pill taking and, thus, higher levels of protection against HIV infection.

Sexual behavior and risk compensation

iPrEx OLE offers a unique opportunity to observe the effects of the use of Truvada PrEP on the sexual risk-taking behavior of study participants during 72 weeks.  Sexual behavior is assessed by a behavioral questionnaire applied at the enrollment visit and every 12 weeks afterwards.  The questionnaires will be applied by computer assisted self-applied interview (CASI).


None of the participants who became HIV positive in the iPrEx study and who received the study drug showed resistance to tenofovir or emtricitabine, the components of Truvada.  The limited evidence of drug resistance encountered in the iPrEx study was all found in people who were already HIV-positive at the time they enrolled in the study, or was related to infection with a strain of HIV that was already resistant to some HIV therapies.  More information about the resistance findings from the iPrEx study is available here. 

iPrEx OLE continues monitoring participants who become HIV-positive during the study for any signs of HIV resistance.  This monitoring includes Allele Specific PCR (AS PCR), which is designed to capture even very low levels of resistance. 

Bone Mineral Density (BMD)

The use of antiretroviral therapy for the treatment of HIV infection is known to decrease bone mineral density (BMD), usually by 2 to 4% on average.  In HIV treatment, loss of bone mineral density typically occurs in the first six to 12 months of treatment and does not progress thereafter. 

The iPrEx BMD and fat distribution sub study was designed to identify the effects of Truvada on bone density or body fat distribution in healthy people not infected with HIV.  iPrEx found that bone mineral density tended to decrease by up to 1% among participants receiving Truvada in the study.  This was a modest but statistically significant difference compared to the placebo group; however this decrease was not associated with any clinical harm; there was no difference in fractures between the Truvada and placebo groups in iPrEx in data collected through week 24 of the study.  Data from longer periods of follow up are coming and will be reported. iPrEx OLE also continues observation to determine whether the bone loss measured to date stabilizes, increases or is reversed. More information about the BMD sub study findings is available here.


Viral hepatitis is the inflammation of the liver caused by a virus. The viruses that cause hepatitis types B and C (HBV, HBC) are transmitted through the body fluids of an infected person to an uninfected person – for example, through unprotected sexual intercourse, sharing needles or syringes or during childbirth. The iPrEx study offered vaccination against HBV vaccination for all HBV-susceptible individuals enrolled in the randomized phase of the study.

Because both components of Truvada, tenofovir and emtricitabine, are active against HBV, the iPrEx study monitored, and iPrEx OLE continues to monitor individuals who are HBV surface antigen positive at the time of enrollment to look for any impact of Truvada on HBV infection.  

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