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A tale of two trials: how adherence is everything in PrEP
Gus Cairns, 2012-03-06 19:00:00
Adherence makes all the difference to the efficacy of pre-exposure prophylaxis (PrEP), the 19th Conference on Retroviruses and Opportunistic Infections (CROI) heard today.
Further data were presented from two trials of PrEP (giving anti-HIV drugs to HIV-negative people to prevent infection), which announced dramatically different results last year.
In April 2011, the FEM-PrEP study found that giving HIV-negative women tenofovir/FTC (Truvada) pills to prevent their acquiring HIV was totally ineffective: there was no difference in HIV incidence between women taking Truvada and women taking placebo.
In July 2011, however, the Partners PrEP study found that Truvada was 73% effective in preventing HIV transmission between heterosexual partners of different HIV status.
How do we explain why giving HIV-negative women antiretroviral pills made no difference to the HIV infection rate in one trial, but prevented at least two in every three infections in the other? The difference, it appears, is that in the Partners PrEP trial, adherence to the study medication was very high, whereas in FEM-PrEP, despite counselling and support, less than half the women took their PrEP pills regularly.
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