for after accidental exposure prevention (occupational or sexual), in Brazil, it is recommended the use of contomitante:

Tenofovir (TDF) + lamivudine (3TC) + atazanavir (ATV / r) for 28 days.

Dear Dr Moise Bello,

There are 2 situations that come to mind where Tenofovir (Viread) can be used for HIV prevention. The first situation has been mentioned above discussed above by Dr Wendel Mombaque Dos Santos . 

The second situation includes serodiscordant couples. These are couples where one partner is positive while the other is negative.

Here too there are 2 strategies where Tenofovir has been used. New WHO guidelines recommend  offering antiretroviral therapy to the HIV positive partner, regardless of his/her own immune status (CD4 count), to reduce the likelihood of HIV transmission to the HIV negative partner. Up to 50% of HIV-positive people in on-going relationships have HIV-negative partners (i.e. they are in serodiscordant relationships). Of those HIV-positive individuals who know their status, many have not disclosed their HIV status to their partners, nor do they know their partners’ HIV status. Consequently, a significant number of new infections occur within serodiscordant couples.

The second strategy looked at giving Tenofovir alone or Tenofovir with Emtricitabine or even Tenofovir gel (vaginal application) to the uninfected partner in a serodiscordant relationship. Since 2010 four randomized controlled trials of oral PrEP have produced evidence of reduction in transmission rate in this situation. These included the The iPrex study (TDF+ emtracitibine, in in high-risk men who have sex with men), the TDF2 trial ( same combination in high-risk heterosexuals) and 2 other trials (FemPrEP & Partners PrEP) that were stopped prematurely. All trials showed a reduction in HIV transmission rate of 40-70%.

Hope this helps

regards

Can Viread be used for HIV Prevention? - ResearchGate. Available from: https://www.researchgate.net/post/Can_Viread_be_used_for_HIV_Prevention [accessed Sep 22, 2015].

Dr. Bello,

In at least one of the trials mentioned tenofovir alone (Viread) was less effective as an HIV pre-exposure prophylaxis than the combination tenofovir/emtricitabine (brand name Truvada). Thus, for high risk individuals Truvada would be the medication of choice. In some of the clinical trials mentioned, the Partners PrEP study for example, analysis of those who were adherent to the once-daily oral regimen of Truvada attained over 90% protection against HIV infection, placing Truvada on par with condoms for efficacy if used daily. However, keep in mind that Truvada does not protect against other STDs or unwanted pregnancy. A clinical trial conducted in Thailand showed that oral pre-exposure prophylaxis (tenofovir) was partially effective at preventing HIV transmission among injection drug uses. A recent review article on PrEP for sexually acquired HIV risk management can be found at the following link: Wilton et al 2015, HIV/AIDS Research and Palliative Care.   http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4422285/pdf/hiv-7-125.pdf   New York State has developed comprehensive clinical guidelines for provision of Truvada for PrEP. See here: http://www.hivguidelines.org/clinical-guidelines/pre-exposure-prophylaxis/guidance-for-the-use-of-pre-exposure-prophylaxis-prep-to-prevent-hiv-transmission/