Pre-exposure prophylaxis (or PrEP) is a way for people who do not have HIV but who are at very high risk of getting HIV to prevent HIV infection by taking a pill every day. The pill (Truvada®) contains two medicines (tenofovir and emtricitabine) that are used in combination with other medicines to treat HIV. When someone is exposed to HIV through sex or injection drug use, these medicines can work to keep the virus from establishing a permanent infection.
When taken daily, PrEP is highly effective for preventing HIV. Studies have shown that PrEP reduces the risk of getting HIV from sex by about 99% when taken daily. Among people who inject drugs, PrEP reduces the risk of getting HIV by at least 74% when taken daily. PrEP is much less effective if it is not taken consistently.
As PrEP only protects against HIV, condoms are important for the protection against other STDs.
How does PrEP work?
What is the difference between PrEP and PEP?
- Post = after
- Exposure = coming into contact with HIV
- Prophylaxis = treatment to prevent an infection from happening
Post-exposure prophylaxis (PEP) is an HIV prevention strategy where HIV-negative individuals take HIV medications after coming into contact with HIV to reduce their risk of becoming infected. PEP is a month-long course of drugs and must be started within 72 hours after possible exposure.
Who does PrEP work for
PrEP has been shown to help reduce HIV infection risk in multiple studies. The iPrEx trial showed that PrEP reduces the risk of HIV infection among gay and bisexual men and transgender women. Two large trials, Partners PrEP and TDF2, showed that PrEP also reduces the risk of HIV infection among heterosexual men and women. The Bangkok Tenofovir Study demonstrated that PrEP works for people who inject drugs.
Effectiveness
Truvada for PrEP provides 92%-99% reduction in HIV risk for HIV-negative individuals who take the pills every day as directed. If a daily dose is missed, the level of HIV protection may decrease. It only works if you take it. People who use PrEP correctly and consistently have higher levels of protection against HIV.
According to data analysis from the iPrEx study that found PrEP to be effective:
- For people who take 7 PrEP pills per week, their estimated level of protection is 99%.
- For people who take 4 PrEP pills per week, their estimated level of protection is 96%.
- For people who take 2 PrEP pills per week, their estimated level of protection is 76%.
There are not enough data available to provide specific timing guidance on non-daily use, so the FDA recommends PrEP be used daily to achieve the highest level of protection.
A few things to note:
- When starting PrEP, it takes at least seven days to reach high levels of protection against HIV.
- When stopping PrEP, individuals should continue using PrEP for four weeks after the last significant exposure.
- PrEP does not protect against other sexually transmitted infections (STI) or pregnancy. It is not a cure for HIV.
Medication options for PrEP
Two medications, sold under the brand names Truvada® and Descovy® are approved for daily use as PrEP to help prevent a person without HIV from getting the virus from sex or injection drug use. You need to discuss your individual needs with your doctor and consider the possible side effects of each drug.
Truvada and Descovy belong to a drug class known as NRTIs, which inhibit and block the virus enzyme called reverse transcriptase. By blocking the action of reverse transcriptase, both drugs in combination with another ARV work together to prevent HIV from multiplying in the body. Both drugs are highly effective in reducing the amount of HIV in the T-cells (white blood cells).
Truvada®
Truvada is an NRTIs drug designed to intercept and inhibit or block the HIV virus enzyme called reverse transcriptase. This enzyme actively infects the DNA and uses it to make copies of the virus. Once these cells are infected, the body’s immune function becomes weaker as the viral load count increases.
Truvada, combined with another ARV medicine, work together to prevent the virus from increasing or replicating in the CD4 cells. The more a patient uses Truvada, the more its concentration in the body increases and becomes highly effective in reducing the amount of HIV in the T-cells (white blood cells).
As PrEP, Truvada intercepts the virus before it enters into the body. PrEP is an effective strategy where the active substances in Truvada stay alert to kill the virus in its early stages before it inhibits the cell DNA causing AIDS.
- You must be HIV-negative before you start and while taking TRUVADA for PrEP. Do not take TRUVADA to reduce the risk of getting HIV-1 unless you are confirmed to be HIV-negative.
- Get tested for HIV-1 immediately before and at least every 3 months while taking TRUVADA.
- If you think you were exposed to HIV-1, tell your healthcare provider right away.
- Many HIV-1 tests can miss HIV-1 infection in a person who has recently become infected. If you have flu-like symptoms, you could have recently become infected with HIV-1. Tell your healthcare provider if you had a flu-like illness within the last month before starting or at any time while taking TRUVADA.
- Symptoms of new HIV-1 infection include tiredness, fever, joint or muscle aches, headache, sore throat, vomiting, diarrhea, rash, night sweats, and/or enlarged lymph nodes in the neck or groin.
- You must continue to use safer sex practices. Just taking TRUVADA for PrEP may not keep you from getting HIV-1.
- Do not miss any doses of TRUVADA. Missing doses may increase your risk of getting HIV-1 infection.
Serious side effects of TRUVADA may also include:
- Kidney problems, including kidney failure. Your healthcare provider should do blood and urine tests to check your kidneys before and during treatment with TRUVADA. If you develop kidney problems, your healthcare provider may tell you to stop taking TRUVADA.
- Too much lactic acid in your blood (lactic acidosis), which is a serious but rare medical emergency that can lead to death. Tell your healthcare provider right away if you get these symptoms: weakness or being more tired than usual, unusual muscle pain, being short of breath or fast breathing, stomach pain with nausea and vomiting, cold or blue hands and feet, feel dizzy or lightheaded, or a fast or abnormal heartbeat.
- Severe liver problems, which in rare cases can lead to death. Tell your healthcare provider right away if you get these symptoms: skin or the white part of your eyes turns yellow, dark “tea-colored” urine, light-colored stools, loss of appetite for several days or longer, nausea, or stomach-area pain.
- Bone problems, including bone pain, softening, or thinning, which may lead to fractures. Your healthcare provider may do tests to check your bones.
Common side effects in people taking TRUVADA for PrEP are headache, stomach-area (abdomen) pain, and decreased weight. Tell your healthcare provider if you have any side effects that bother you or do not go away.
Descovy®
Descovy® for PrEP is recommended to prevent HIV for people at risk through sex, excluding people at risk through receptive vaginal sex. Because Descovy has not yet been studied for HIV prevention for receptive vaginal sex, it may not be appropriate for some people.
Descovy works the same way as Truvada. It is a nucleoside reverse transcriptase inhibitor which actively undergoes intracellular metabolism where tenofovir alafenamide is first hydrolyzed to tenofovir-alanine, and converted into parent tenofovir.
The action of tenofovir (tenofovir diphosphate) as it enters the body is to inhibit the activity of virus reverse transcriptase, causing viral DNA chain termination. Once the virus’ active action is terminated, there is no more replication of the virus and the CD4 cell count begins to increase in number, restoring the body’s immune function.
Note that Descovy doesn’t cure HIV. It reduces its viral count in the T-cells and the more you consistently use this medication, the more the viral load count decreases.
Before and while taking DESCOVY for PrEP:
- You must be HIV-negative before you start and while taking DESCOVY for PrEP. You must get tested for HIV-1 immediately before and at least every 3 months while taking DESCOVY. If you think you were exposed to HIV-1, tell your healthcare provider right away. They may want to do more tests to confirm that you are still HIV-negative.
- Many HIV-1 tests can miss HIV-1 infection in a person who has recently become infected. Tell your healthcare provider if you had a flu-like illness within the last month before starting or while taking DESCOVY. Symptoms of new HIV-1 infection include tiredness, fever, joint or muscle aches, headache, sore throat, vomiting, diarrhea, rash, night sweats, and/or enlarged lymph nodes in the neck or groin.
- DESCOVY by itself is not a complete treatment for HIV-1. Do not take DESCOVY for PrEP unless you are confirmed to be HIV-1 negative.
- DESCOVY does not prevent other sexually transmitted infections (STIs). Practice safer sex by using a latex or polyurethane condom to reduce the risk of getting STIs.
- To further help reduce your risk of getting HIV-1:
- Do not miss any doses of DESCOVY. Missing doses may increase your risk of getting HIV-1.
- Know your HIV status and the HIV status of your partners. If your partner is living with HIV, your risk of getting HIV is lower if your partner consistently takes HIV treatment every day.
- Get tested for other STIs. Some STIs make it easier for HIV-1 to infect you.
- Talk to your healthcare provider about all the ways to help reduce HIV risk.
DESCOVY can cause serious side effects:
- Worsening of hepatitis B (HBV) infection. Your healthcare provider will test you for HBV. If you have HBV and stop taking DESCOVY, your HBV may suddenly get worse. Do not stop taking DESCOVY without first talking to your healthcare provider, as they will need to check your health or give you HBV medicine.
Who should not take DESCOVY for PrEP?
Do not take DESCOVY for PrEP if you:
- Already have HIV-1 or if you do not know your HIV-1 status. If you have HIV-1, you need to take other medicines with DESCOVY to treat HIV-1. If you have HIV-1 and take only DESCOVY, your HIV-1 may become harder to treat now and in the future.
What are the other possible side effects of DESCOVY for PrEP?
Serious side effects of DESCOVY may also include:
- Kidney problems, including kidney failure. Your healthcare provider should do blood and urine tests to check your kidneys before and during treatment with DESCOVY. If you develop kidney problems, your healthcare provider may tell you to stop taking DESCOVY.
- Too much lactic acid in your blood (lactic acidosis), which is a serious but rare medical emergency that can lead to death. Tell your healthcare provider right away if you get these symptoms: weakness or being more tired than usual, unusual muscle pain, being short of breath or fast breathing, stomach pain with nausea and vomiting, cold or blue hands and feet, feel dizzy or lightheaded, or a fast or abnormal heartbeat.
- Severe liver problems, which in rare cases can lead to death. Tell your healthcare provider right away if you get these symptoms: skin or the white part of your eyes turns yellow, dark “tea-colored” urine, light-colored stools, loss of appetite for several days or longer, nausea, or stomach-area pain.
Common side effects in people taking DESCOVY for PrEP are diarrhea, nausea, headache, fatigue, and stomach pain. Tell your healthcare provider if you have any side effects that bother you or do not go away.
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