It all began with a 1994 study that showed antiretrovirals given to HIV-positive pregnant women before and during childbirth – as well as to the child upon delivery – reduced the risk of mother-to-child HIV transmission by 50%. Next were the post-exposure prophylaxis guidelines issued by the Center for Disease Control and Prevention in 1998, recommending an antiretroviral regimen for healthcare workers after unintended HIV exposure. Then, 2006 brought exciting data gleaned from a study of monkeys who remained uninfected after repeated exposure to a HIV-like virus as a result of taking the antiretroviral drugs tenofovir and emtrictabine. These studies raised the question: Can drugs prevent HIV? After recent unimpressive results in vaccine and microbicide tests, scientists’ leading hope for stopping HIV infection before it starts seeks to answer that question with pre-exposure prophylaxis, or PrEP.
By the middle of next year, close to 15,000 individuals will be enrolled in PrEP trials. That’s more people than all HIV vaccine and microbicide trials combined. In the PrEP approach, an oral antiretroviral agent (specifically, Viread or Truvada) is taken daily to prevent HIV infection. In theory, this method inhibits HIV replication and permanent infection from the moment the virus enters the body. If proven safe and effective, PrEP could significantly reduce the risk of HIV infection for high-risk individuals all over the world. It would be particularly advantageous for individuals in serodiscordant relationships as well as those unable to negotiate other proven protective measures such as condom use. Perhaps most importantly, PrEP would represent the first female-initiated intervention method.
Currently, three studies conducted by the CDC are underway to test the safety and effectiveness of PrEP. In Thailand, injection drug users are using once-daily Viread. In Botswana, young heterosexual men and women are taking once daily Truvada, and in the US, once-daily Viread is being tested among men who have sex with men.
PrEP is quickly becoming a reality. Over the course of 7 years, the CDC will spend an estimated $53 million researching PrEP. Most importantly, the CDC has recently urged public health leaders to begin planning for PrEP implementation. The time has come to discuss the optimal use and delivery of PrEP if found effective. PrEP raises particularly challenging questions that need attention now. How will we ensure that individuals use PrEP in concert with other proven preventative strategies? Some people may refuse to use condoms if they learn that their partner is taking PrEP and, theoretically, protected from HIV transmission. No single strategy will likely be 100% effective against HIV infection, and reducing transmission will require integration of all biomedical and behavioral methods. How will healthcare providers ensure that PrEP is used before exposure, and not after infection, to prevent drug-resistant HIV? Who exactly would be prescribed PrEP? Would people be required to prove that they are at "high risk," and if so, will that lead to their being stigmatized? What will happen if an individual disregards instructions for daily use and takes the pill before a night on the town? Will this ineffective so-called “disco dosing” become rampant? Already, rumors are emerging of new drug cocktails of Truvada, Viread, Viagra and Ecstasy that are being sold in gay dance clubs.
Clearly, this new strategy will not be a panacea for the difficult issues involved in the HIV pandemic, including stigma, the sexuality of young people, drug use, homophobia and the sex industry. PrEP may one day be an important response to AIDS, but that response will never be equitable nor ultimately successful unless we begin planning for it now.