I recently had an exposure to HIV, the status of the person was unknown.

I presented at the hospital after 12 hours of exposure and was given 'Truvada' as the sole medication.

I previously had an exposure in 2007 and was given 'Combivir' as a sole medication.

In the absence of Zidovudine 300mg with Truvada (or Tenofovir 300mg with Combivir) is the effectiveness of PEP reduced, and should I be asking/insisting on a prescription for the other antiretroviral Zidovudine in my case?

Guidelines for use of medications to prevent HIV transmission after sexual contact (non-occupational exposure) called nPEP have been established by the CDC and various state health departments. Use of medications are based on a few basic principles: There should be a real or potential exposure; the medications should be started as soon as possible (but no later than 72 hours after the exposure); prevention is better if more than one drug is used; and treatment should be for 4 weeks.

Since the HIV-status of your partner is not known, the risk for HIV transmission may not exist at all..so deceisions about whether or not to start treatment are based on the likelihood that the person might be infected (i.e if the person is a man who has sex with men, injection drug user, or a commercial sex worker). The treatment with either combivir (2 meds: zidovudine and lamivudine) or truvada (2 meds: tenofovir and emtricitabine) would be expected to be equivalent in benefit (truvada is likely to have fewer short-term side effects). The 2 pills should not be combined together since lamivudine and emtricitabine have essentially the same effect on the virus and would not add any benefit to each other.

Most data on the use of nPEP has been based on single or 2 drug therapy, there is little information to indicate whether the addition of a third NRTI (adding zidovudine to truvada or tenofovir to combivir) would make a difference. To avoid these issues, some guidelines (New York for example (http://www.hivguidelines.org/GuideLine.aspx?pageID=78&guideLineID=2) make a blanket recommendation to use a triple combination of (Truvada + zidovudine; or Combivir + tenofovir). California guidelines recommend a 2-drug combination (such as Combivir or truvada) alone (http://www.cdph.ca.gov/programs/aids/Documents/RPT2004OfferingPEPFollowingNonOccupExp2004-06.pdf).

While there is no concensus on how many NRTIs should be used, the most important matter is that the therapy be started ASAP after exposure and taken for 28 days. If that is followed the risk of postential transmission is greatly reduced.

Best, Joe