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July 18, 2011

More studies show success of pre-exposure prophylaxis in preventing HIV transmission

More studies show success of pre-exposure prophylaxis in preventing HIV transmission

The iPrEx study results demonstrated a 44% reduction in HIV transmission among men who have sex with men with the use of pre-exposure prophylaxis, however a reduced risk of transmission was not apparent in the Fem-PrEP study among high-risk women. Many researchers have been awaiting results from other pre-exposure prophylaxis trials before implementation of PrEP.

During a unique session at the IAS Conference in Rome dedicated to Treatment as Prevention, the long awaited results from both the TDF2 and the Partners PrEP studies were made available:

Michael Thigpen of the CDC announced the results of the TDF2 study. This was a double-blind placebo-controlled randomized clinical trial comparing TDF-FTC to placebo in 1219 HIV-negative men and women, ages18-39 in Botswana. Participants were screened for HIV at baseline and monthly thereafter for 12 months. All participants received HIV risk reduction counseling and testing and treatment of sexually transmitted infections. Adherence was monitored by self-report, pill counts and drug levels. There were 9 HIV-infections seen in the TDF-FTC group compared with 24 infections in the placebo group. An overall protective efficacy 62.6% (95% CI 21.5 to 83.4, p=0.0133) was seen in the intent to treat analysis. One participant who had unrecognized acute HIV infection at enrollment and who was started started on TDF-FTC developed several mutations including K65R, M184V and A62V. One participant with HIV infection who was assigned to the placebo group was noted to have K65R mutation. Daily TDF-FTC was seen to be effective and safe for prevention of HIV infection among heterosexual clients. The development of resistance mutations in the subject assigned to TDF-FTC with unknown acute infection underscores the need for screening for acute HIV infection before prescribing PrEP.[1]

Jared Baeten of The Partners PrEP Study Team presented the results from the second study evaluating Pre-Exposure Prophylaxis (PrEP) for HIV-1 that was stopped 1.5 years prematurely by the DSMB due to clear evidence of protection to subjects in the treatment arms as compared to the placebo arm. This study was a phase lll randomized double-blind placebo controlled trial of daily oral tenofovir (TDF) and emtricitabine/tenofovir (FTC/TDF) for the prevention of HIV infection in serodiscordant partnerships. The study was conducted among heterosexual African men and women at several sites in Kenya and Uganda. HIV negative participants received monthly HIV and pregnancy testing and 3 monthly laboratory monitoring. HIV-positive participants received HIV primary care services. All couples received risk reduction counseling, free condoms and screening and treatment for STIs. The regimen was well tolerated with 97% adherence reported to treatment groups and placebo. 78 HIV infections were acquired as of May 31, 2011, 18 in the TDF arm, 13 in the TDF-FTC arm and 47 in placebo. This was a 62% reduction for TDF (34-78%) 73% for TDF-FTC (49-85%). Of note the investigators found no evidence of increased adverse effects beyond the first month or evidence of risk compensation. This study offers further evidence of evidence for pre-exposure prophylaxis in reducing HIV infections. After the Partners PrEP study was stopped prematurely all clients receiving placebo were offered active PrEP. The study will be continued to evaluate safety and resistance issues in the TDF vs FTC/TDF PrEP arms. At the conclusion of the presentation the investigators discussed the need for demonstration projects to further assess the effectiveness of PrEP as part of combination HIV prevention.[2]

1. Thigpen M, et al. Daily oral antiretroviral use for the prevention of HIV infection in heterosexually active young adults in Botswana: results from the TDF2 study [Oral Abstract]. Presented July 18, 2011 at the 6th IAS Conference on HIV Pathogenesis, Treatment and Prevention, Rome, Italy. Abstract WELBC01

2. Baeten J. Antiretroviral Pre-Exposure Prophylaxis for HIV-1 prevention among heterosexual African men and women: the Partners PrEP Study [Oral Abstract]. Presented July 18, 2011 at the 6th IAS Conference on HIV Pathogenesis, Treatment and Prevention, Rome, Italy. Abstract MOAX0106.

Source: Reporting for PRN news from Rome, Italy: Anita Radix, MD