Jan 29, 2010
Hi Dr. Frascino, I was wondering why there is such a lack of studies concerning the length of time that PEP be taken. A large majority of the justification for the 4-week regimen seems to be coming from one or perhaps a few fairly dated studies with SIV that determined PEP was most effective if taken for 4 weeks. Then I came across some information purported by Dr. Gabriel Torres in NYC in which he stated there was probably no benefit to taking PEP for more than 2 weeks. I also came across an article that tested giving monkeys truvada in only 2 doses- one either right before or after infection and another about a day later or so. In many of the trials over half the monkeys were protected even though they were exposed many times to ensure the virus was transmitted. Are you aware of any ongoing research that sheds light on perhaps a shorter time for PEP regimens? Thanks.
Response from Dr. Frascino
Designing and conducting studies to determine the optimal duration of PEP is extremely challenging, due to the confounding variables involving the source (viral load, viral strain, etc.), the host (immune integrity, concurrent illnesses, age, etc.), PEP regimen, and type of exposure (vaginal, anal, oral, intravenous drugs, etc.). The study would also need to be very large to be statistically significant to prove PEP efficacy, as most HIV exposures do not lead to transmission. The 28-day PEP regimen was determined by a number of studies, including an early one on healthcare workers. PEP efficacy was also suggested by mother-to-child transmission studies.
As for the Simian studies (SIV), a 50% protective rate, while significant, is still not all that great.
My advice is to stick to the 28-day regimen per the PEP guidelines.
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