Pre-exposure prophylaxis (PrEP)
Pre-exposure prophylaxis, or PrEP, is a way for an HIV-negative person who is at risk of HIV infection to reduce their risk of becoming infected with HIV. It involves taking anti-HIV drugs on a regular basis. PrEP provides only partial protection from HIV infection and is not intended to replace consistent condom use, new needles or other ways of preventing HIV. PrEP has not been approved by Health Canada; however, one type of PrEP (daily oral Truvada pills) has been approved in the United States. This form of PrEP may be available in Canada from doctors who are willing to prescribe it “off-label.” Truvada as PrEP is much less effective at reducing the risk of HIV transmission if pills are not taken daily.
What is PrEP?
PrEP is a new HIV prevention method. It involves an HIV-negative individual taking anti-HIV drugs in an effort to reduce their risk of becoming infected with HIV. A person at risk of infection needs to take anti-HIV drugs on a regular basis—starting before being exposed to HIV and continuing afterwards. A person using PrEP needs to take the drugs exactly as directed. They also need to commit to regular doctor’s appointments, so that any side effects can be monitored and they can be tested for HIV and other sexually transmitted infections (STIs).
There are several types of PrEP being investigated. PrEP drugs may be available in a variety of formats, including pills (oral PrEP), a vaginal/rectal gel (topical PrEP), or injections. The drugs may need to be taken every day, or before and after sex, or intermittently (once or twice a week).
Does PrEP work?
Only one form of PrEP has been approved for HIV prevention in the United States (although not in Canada). The approved form of PrEP is the use of a daily pill containing the anti-HIV drugs tenofovir and emtricitabine (known by the brand name Truvada). It has been approved for gay men and other men who have sex with men (MSM) and heterosexual men and women who are at risk of sexual transmission of HIV. The U.S. Centers for Disease Control and Prevention (CDC) has developed guidelines for the prescription of daily Truvada as PrEP to MSM, heterosexual men and women, and people who use injection drugs. However, PrEP only provides partial protection from HIV infection and is not intended to replace other forms of HIV prevention. Research shows that adherence is crucial for oral PrEP to work.Many other forms of PrEP are in different stages of research. There are studies looking at the safety and effectiveness of a particular type of PrEP (such as pills or gels) in a specific population (such as gay and bisexual men, people who use injection drugs, or heterosexual men and women). Some types of PrEP have been found to be effective at reducing the risk of HIV transmission for specific populations. The research findings for each form of PrEP are summarized below.
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Pills (oral PrEP)
In some research studies, HIV-negative people are asked to take an anti-HIV pill every day to see if it will provide some protection against HIV infection. This type of PrEP is similar to the birth control pills women take daily to prevent pregnancy or the medications people travelling to certain tropical countries take daily to prevent malaria. These studies suggest that certain forms of daily oral PrEP can reduce the sexual transmission of HIV for HIV-negative men and women, including gay and bisexual men, and heterosexual men and women .
In one study, HIV-negative gay and bisexual men who were asked to take an anti-HIV pill (Truvada) every day reduced their overall risk of HIV infection by 44%. Men who said they took the pill more consistently reduced their risk by as much as 73%. Additional analysis suggests the level of protection may be even higher among those who took Truvada every day, as determined by drug levels in the blood. In other studies, the same PrEP strategy (daily Truvada) provided similar levels of protection for heterosexual men and women. An anti-HIV pill containing tenofovir alone was also found to be effective for heterosexual men and women and people who use injection drugs.
Surprisingly, two studies found that an anti-HIV pill (Truvada) taken every day did notwork for women. However, women in these studies were not taking PrEP consistently.
Vaginal gels (topical PrEP)
Other research studies are looking at gels that contain anti-HIV drugs. One study found that HIV-negative women who applied an anti-HIV gel (containing tenofovir) into the vagina before and after sex reduced their risk of infection by 39%. Women who applied the gel more consistently reduced their risk of infection by as much as 54%. Surprisingly, another study found daily use of the same gel did not work for women. However, women in this study were not using the gel consistently.
More studies are needed to determine if a vaginal gel works and to determine whether the gel would work if used rectally.
Long-lasting injections and intravaginal rings
Small research studies are investigating long-lasting forms of PrEP, such as injections and intravaginal rings, which would only need to be used monthly. It will be several years before large studies are conducted to determine whether these forms of PrEP work.
Is PrEP intended to replace condoms and other ways of preventing HIV?
No. People who use PrEP may be partially protected from HIV infection but not fullyprotected. Also, PrEP is not expected to protect against other STIs, such as gonorrhea, chlamydia or syphilis, or other infections that are transmitted by sharing injection drug use equipment, such as hepatitis C. This means that it will still be possible for a person using PrEP to become infected with HIV, hepatitis C and other STIs.
People who use PrEP will also need to use other prevention methods, such as condoms and new needles, to reduce the risk of infection with HIV or other STIs. If people using PrEP stop using condoms or new needles, their risk for HIV infection may actually increase because PrEP may be less effective than other prevention methods.
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Is PrEP a “morning-after” pill for people accidentally exposed to HIV?
No. With PrEP, a person will need to recognize that they are at risk of infection and begin taking anti-HIV drugs on a regular basis before an exposure occurs.
For people who may have been accidentally exposed to HIV (at work or through unprotected sex, for example), there is another prevention method called post-exposure prophylaxis (PEP). With PEP, an HIV-negative person needs to start taking a combination of anti-HIV drugs as soon as possible (within 72 hours) after a potential exposure to HIV and must continue taking the drugs every day for four full weeks.
It is easy to confuse PEP and PrEP because they both involve the use of anti-HIV drugs by HIV-negative people to prevent HIV infection.
What are the advantages of PrEP?
PrEP provides an additional prevention method that can be used in combination with other prevention strategies, to help protect a person from HIV infection.
Although PrEP is not intended to replace other methods for HIV prevention, in certain situations it may provide an alternative form of prevention for those who do not use condoms or new needles regularly. For example, PrEP may provide another method of protection for those who are unable to negotiate condom use with their partner(s), people in serodiscordant relationships (where one partner is HIV-negative and the other is HIV-positive) who wish to conceive a child, or people who inject drugs but are not able to obtain new needles.
What are some of the safety concerns associated with PrEP?
A person could develop drug resistance if they are HIV-positive (and don’t know it) when starting PrEP or they become HIV-positive while taking PrEP. Once a person’s HIV becomes resistant to the PrEP drugs, those same anti-HIV drugs may not work for treating their HIV.
A person who uses PrEP needs to follow the medication schedule that their doctor recommends. If the schedule is not followed—if a person misses too many doses or experiments with another schedule—then the risk of becoming infected and developing drug resistance can increase.
Anti-HIV drugs cause side effects, which may negatively affect a person’s quality of life and ability to adhere to their medication schedule. Although the drugs selected for PrEP studies are generally better tolerated than other drugs used to treat HIV, they are still capable of causing mild to severe side effects. Some of the possible side effects include nausea, vomiting, diarrhea, headache and dizziness. PrEP may also cause decreases in kidney function and bone density. However, research suggests that side effects while using PrEP are generally mild and uncommon.
A false sense of security
Another concern is that people may feel a false sense of security when using PrEP and decide to engage in more risky activities. If people using PrEP decide to have sex with more partners, use condoms less often or share needles more frequently, then their overall risk for HIV infection (and other STIs) may increase because PrEP does not provide complete protection.