PrEP (Pre Exposure Prophylaxis) is the use of anti-retroviral drugs taken by HIV negative people to prevent transmission of HIV. When a person without HIV takes it, it can prevent them getting HIV. In Australia it is mainly used by men having high risk sex with other men (eg without condoms, in situations with high HIV prevalence). EPIC NSW is a trial where the vast majority of places will be for men who have sex with men. PrEP may be appropriate for heterosexual people in a sero-different relationship or having sex without condoms with a positive person who is not undetectable or is not on treatment.
Taking Truvada at least 2 hours before sex and several days after can prevent HIV–but not as well as the longer term daily pill.
Although PrEP has been shown to be effective in preventing HIV infection, long-term adherence can be challenging. This has lead researchers to look for options to the to the one-a-day pill.
Researchers at the University of Paris Dederot evaluated the possibility of an “on demand” regimen using results from the IPERGAY study. The results, announced at CROI demonstrate that taking two pills between two to 24 hours before sex and one additional pill each of the following two days, does prevent HIV transmission with an HIV incidence reduction of 86 percent in those taking it as described. This method of taking PrEP isn’t perfect but presents a viable alternative for long-term daily adherence.
Regardless, the Center for Disease Control and Prevention in the States recommends that PrEP be taken at least seven days before a possible exposure while urging PrEP users to stick to daily regimens. “While two pills the day before sex is better than none,” explained Dr. Robert Grant, medical director for the San Francisco AIDS Foundation, “the highest level of protection comes after five to seven daily doses for rectally exposed men (and 20 daily doses for women)…Two tablets before infrequent sex probably does not provide the same high level of protection that we see with daily dosing.”
At this point, PrEP on demand has not been approved by the FDA and therefore cannot be prescribed by doctors.