July 17, 2012
PrEP Talk 101
by Trenton Straube
A pill prevents getting HIV? Here's what you need to know about Truvada, the HIV med the FDA just approved as pre-exposure prophylaxis (PrEP).
The HIV prevention toolbox just got a headline-grabbing addition. On July 16, the FDA approved Truvada as a pill that certain HIV-negative people can take to prevent them from getting HIV through sex. When taken as pre-exposure prophylaxis, or PrEP, Truvada, which is manufactured by Gilead Sciences, is supposed to be used daily along with safer-sex practices such as condoms and regular HIV testing. How does Truvada as PrEP work? Who is a good candidate for it, and what are the risks? For answers, AIDSmeds spoke with three specialists: Jared Baeten, MD, PhD, an associate professor of global health and medicine at the University of Washington at Seattle and co-leader of the Partners PrEP study; Gal Mayer, MD, the medical director of the Callen-Lorde Community Health Center in New York City, whose primary focus is gay men; and Albert Liu, MD, MPH, the director of prevention interventions at the San Francisco Department of Public Health and also the medical director of the iPrEX study (more details on these studies later). Together, we break down the basic science and real-world application of Truvada as PrEP.
How does Truvada as PrEP work?
To better understand this, it’s helpful to know how HIV meds work in someone who is positive. A person living with HIV takes at least three or four HIV drugs—called combination antiretroviral therapy—that work together to keep the virus from replicating. The meds don’t seek out the virus and attack it directly; rather, they each halt different steps of the complicated process in which the virus uses immune cells to make new copies of itself. A similar thing happens in PrEP. “Truvada is a combination pill of two HIV medications (tenofovir and emtricitabine) commonly used for HIV treatment,” explains Albert Liu. “When taken as PrEP, Truvada can block HIV replication from occurring and prevent HIV from establishing infection in the body.”
Why can’t a person only take Truvada before or after sex, as opposed to every day?
“It takes a while for Truvada to build up to levels in the body that can protect people from HIV infection,” Liu explains. “We don’t yet know exactly how long this takes, but it likely takes at least a few days.” Additional studies are exploring this topic and testing alternative dosing schedules, such as four and two times a week. “In the meantime,” Liu stresses, “it is recommended that people take PrEP once a day, as this was how it was tested in previous PrEP studies.” Jared Baeten adds that “it’s also important to have some amount of medication use after exposure.”
And Gal Mayer points out another prevention tactic for people to be aware of: PEP, or post-exposure prophylaxis, which is when a person not on PrEP is possibly exposed to HIV (if a condom breaks, for example) and takes HIV meds to reduce the likelihood of infection. PEP should be started no later than 72 hours after possible exposure, and it’s usually taken for a month; three meds are generally used for PEP instead of the two for PrEP.
What happens if you miss a dose of Truvada as PrEP?
This is a question researchers are still exploring. They aren’t exactly sure how many doses could be missed, or how often, without undercutting protection against HIV. It seems clear that better adherence equals better protection. “Missing one dose of PrEP in someone taking it consistently probably would have no impact,” Baeten says. He makes an analogy with HIV treatment: “We prescribe it for every day, but we know that not everyone uses it every day. Everyone misses a dose once in a while—that’s human nature. But most people who take it on a regular basis still get really strong HIV treatment benefits. So PrEP probably is similar in that way.”
Liu also acknowledges it can be difficult to take PrEP every day. “If you miss a dose,” he says, “you should just try to get back on track with taking a pill a day. If you miss doses frequently, it can be helpful to talk with your clinician who can discuss strategies to help with pill taking. Also, life changes happen, and some people change their mind about taking PrEP. In these cases, your clinician can help work through decisions about whether to continue taking PrEP.”
What do we know about side effects of Truvada as PrEP?
“Rates of side effects were low in PrEP studies of Truvada,” Liu says. “Some people may experience some side effects when they first start taking PrEP. These symptoms are usually mild and often go away or get better after the first month. Most of the time, people who do have side effects experience [gastro intestinal] changes, such as stomach cramps or nausea. There are things people can do to reduce these symptoms, such as taking the medication with food or at night before going to bed. It’s important to talk with your clinician if you’re having side effects, as there are other strategies to help reduce these symptoms.”
“The biggest concerns for long-term use are the effects this medication can have on the kidneys and bone density,” says Mayer, who adds that those problems are uncommon and that most people can take Truvada safely for years. Nonetheless, he monitors his patients for those two issues.
There is talk about drug resistance with PrEP. What does this means, and why is it a concern?
HIV is a tricky virus. It replicates constantly and mutates often. When there is only some HIV medication present, but not enough to halt the replication process—for example, if a person doesn’t take HIV meds daily or doesn’t take enough of them—then the virus can shape-shift to resist them. “In this way,” Mayer notes, “that which does not kill HIV literally makes it stronger.”
Remember that Truvada is made of two HIV meds and that people with HIV usually take a cocktail of three or four meds to control the virus. Well, if a person unknowingly has HIV and starts taking PrEP, it would be like taking an inadequate cocktail treatment and the virus would be able to mutate and become resistant to one of both of the drugs in Truvada. “So it’s important to be sure you’re negative before you start PrEP,” Baeten stresses. “The only people who developed HIV resistance in the PrEP studies so far have been people who were already infected when they started PrEP. They were in the window period”—the weeks between infection and the point at which antibodies become detectable using available tests—“and the researchers didn’t know they had HIV because the tests were negative for HIV.” [See editor's note below.]
Baeten reiterates the lessons from PrEP studies thus far. If people who don’t have HIV start PrEP and adhere to treatment, then PrEP should protect them from HIV. Those who did get HIV were the ones who received placebo in the study or, in many cases, were not taking their Truvada as recommended.
But what about condoms? Won’t guys on PrEP forget about safe sex and start barebacking—and won’t that increase their HIV risk, especially if they’re missing daily PrEP doses?
In the PrEP trials, participants actually reduced their risk-taking actions, but they also received free condoms and lube as well as counseling and screenings for sexually transmitted infections—and they didn’t know whether they were taking an effective medicine or a placebo. Additional studies are now needed, Liu says, to look for changes in risky behavior when PrEP is implemented in the real world.
But some critics are also saying that men who can’t use condoms regularly will not succeed in taking PrEP daily. “I think that will turn out to be wrong,” Mayer says. “Adherence to medication that has almost no side effects can be achieved by incorporating [Truvada] into life’s other rituals. Brush your teeth every morning? Leave your PrEP by your toothbrush and you’ll be less likely to skip doses.
“In contrast,” he says, “using a condom is a complex social interaction. For those who haven’t found a way to incorporate it seamlessly into their sex lives, it may involve two people interrupting a pleasurable experience to remind themselves of an unpleasant reality. You may also have to convince a partner to use it or let you use it, stay hard while putting it on, and then find a way to resume the sex where you left off.
“Despite all that, every day thousands of people use condoms successfully to prevent HIV infection. Because it’s so effective, has no side effects and is so cheap, a condom is still the best way to prevent HIV infection. But I reject the idea that people who can’t use condoms consistently will categorically be unable to adhere to taking PrEP daily. I would even say that those who struggle with condoms and feel bad or anxious about failing to use them correctly, may have tremendous motivation to use PrEP correctly.”
Mayer continues: “Someone who is using condoms consistently and has good safer-sex practices does not need PrEP with Truvada. However, let’s consider the person—call him Joe—who is struggling with condom use, which is true for many men in the gay community. Joe doesn’t want to become infected with HIV but only succeeds at using condoms 50 percent of the time, whether because of drug use, depression, peer pressure or whatever. Currently, Joe is risking HIV infection the other 50 percent of the time. Joe is probably very anxious about acquiring HIV [and is] an excellent candidate for PrEP. Once on daily PrEP, [provided that he uses it daily as prescribed,] he is going to be over 90 percent protected against HIV even when he doesn’t use condoms. So even if his condom use drops to 20 percent because he feels protected by PrEP, there is still a far lower HIV infection risk for him, and in turn, for all Joe’s partners, than without PrEP. But the key is consistent use, which is why it’s important to discuss adherence with Joe and to follow him closely.
“Importantly,” Mayer says, “we should also explore the reasons Joe is having trouble with condoms. If it’s depression, we should also treat Joe’s depression. If it’s drug or alcohol use, we should provide Joe with substance use treatment. We should be aiming to help Joe with the problems he’s having using condoms and working toward the day when Joe won’t need PrEP anymore.
“But I also know that many gay men are having unprotected sex as a personal choice, and not because they’re depressed or have a drug problem. Those men are generally trying to avoid HIV by other strategies: having unprotected sex only with partners who claim to be negative (serosorting), having unprotected sex only when they’re the top (seropositioning), having unprotected sex only with partners they trust, and so on. All those strategies have been proven time and again to be far from fail-proof, and that’s why we see so many gay men becoming infected with HIV. For those men, PrEP could be enormously helpful.
“Do I think a person on PrEP will use condoms less frequently? The studies don’t show that they do, but real life might be very different, and I think some will inevitably use condoms less. But I also think that using PrEP correctly will still be more protective, even with less condom use. Only time will tell.”
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