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By Medical Author: Pallavi Uttekar

By Medical Reviewer: Shaziya Allarakha

Pre-exposure prophylaxis (PrEP) is a course of prescribed medications that people who are at risk of human immunodeficiency virus (HIV) may take to prevent infection. This medication is administered to individuals who have tested negative for HIV but are at a high risk of HIV infection through sexual intercourse or intravenous drug use.

However, antiretroviral therapy (ART) is administered to individuals who have already tested positive for HIV. These individuals do not benefit from either post-exposure prophylaxis (PEP) or PrEP. Therefore, if you have tested positive for HIV, you must take ART, whereas if you are at risk of HIV infection because of your lifestyle, you must talk to your doctor about starting PrEP.

According to the Centers for Disease Control and Prevention (CDC), a daily dose of PrEP can lower the risk of HIV infection by the sexual route by about 99 percent and by sharing needles during drug use by about 74 percent. PrEP protection is maximum at about seven days after starting daily therapy in case of the sexual route and at about 21 days after starting daily therapy in case of individuals who use intravenous drugs and share needles.

It is essential to note that PrEP must be taken as prescribed. Missing doses can increase your risk of HIV. Taking PrEP can cause some side effects such as nausea, vomiting and, in rare cases, liver dysfunction. 

Unless you are allergic to latex condoms, PrEP is not an alternative to condoms. Right and consistent use of condoms is the most cost-effective, efficacious and safe method to prevent HIV risk (by more than 90 percent). Although PrEP can provide very effective protection against HIV, unlike the condom, it does not protect against other sexually transmitted infections (STIs) such as herpes, chlamydia, hepatitis B and C, syphilis and gonorrhea. Moreover, PrEP will not prevent an unwanted pregnancy.

How is PrEP administered?

Pre-exposure prophylaxis (PrEP) must ideally be taken as a daily dose in the manner prescribed by your health-care provider. Currently, the only recommendation by the Centers for Disease Control and Prevention (CDC) for PrEP is the drug named Truvada (a combination pill consisting of two drugs: tenofovir and emtricitabine) to be taken daily.

In some countries, single-dose therapy with tenofovir has been used as PrEP with varying degrees of success. Other antiretroviral drugs such as maraviroc are being studied as possible PrEP alternatives, but efficacy data in these cases are lacking.

On-demand PrEP (2-1-1 PrEP) means taking PrEP (Truvada) only when you are at risk of human immunodeficiency virus (HIV) infection. It is considered effective only in men who have anal sex with men. We do not know yet if on-demand PrEP works in those who have vaginal sex. On-demand PrEP is administered as follows:

• You take two pills about two to 24 hours before the expected time of sex

• Then you take one pill 24 hours after the initial dose

• Then one final pill 24 hours later

Now, if you have anal sex more than 24 hours after taking your first dose (two pills), you need to continue taking one pill every day until you have taken two doses following your last sexual encounter. Then you may stop taking the tablets.

Studies have reported that the 2-1-1 schedule provides some protection for gay and bisexual men when having anal sex without a condom, but the extent of protection is unknown. The effectiveness of on-demand PrEP is unknown in people who inject drugs and share needles. The CDC currently does not recommend the use of on-demand PrEP.

What is the difference between PreP and PEP?