How PrEP For HIV Works
August 27, 2019
PrEP, which stands for pre-exposure prophylaxis, is a medication regimen designed to reduce the chances of infection by the Human Immunodeficiency Virus (HIV) in at-risk patients. The most widely used PrEP medication is a combination of tenofovir disproxil fumarate (TDF) and emtricitabine. While generic versions of PrEP for HIV exist, in the United States, it is sold as “Truvada” by the pharmaceutical company Gilead Science.
When used consistently with appropriate precautions and regular visits to a physician to test for HIV, PrEP can keep patients HIV-free for the duration of their lives.
From HIV to AIDS
HIV spreads via blood, unprotected sex (vaginal, anal, and oral), or from mother to baby (pregnancy, labor, and breastfeeding). The virus cannot be spread through saliva, for instance, with kissing, but it could be spread via transmission of infected blood if there’s an open sore or cut in the mouth of an HIV-positive person or in the mouth of an HIV-negative person when they are kissing an HIV-positive person.
Within two or four weeks of infection, a person with HIV may experience a flu-like illness that is indistinguishable from normal flu. Some people will not experience any symptoms at all. This stage is known as Acute HIV, and HIV levels will be very high as the virus spreads and infects the cells that make up the immune system. During the acute stage, a person is highly contagious.
Following this brief period, a person with HIV will enter a longer latent period known as Chronic or Asymptomatic HIV. This chronic period can last for years or even over a decade without medications, and there might not be any symptoms or illness. HIV levels drop to very low amounts, but the virus is still active and reproducing. A person must take antiretroviral therapy (ART) during this period to keep virus levels down and reduce the chance of transmission to another person. ART can extend the chronic period for several decades.
If a person with HIV does not maintain a consistent ART regimen, their chronic period will end and HIV levels will rise once again. This is when an HIV patient develops Acquired Immunodeficiency Syndrome (AIDS). As HIV finally overwhelms the immune system, a person with AIDS will lose the ability to fight off even minor infections. Something like normal skin bacteria, which would be harmless to a healthy person, may become lethal to a person with AIDS.
How PrEP Works
The goal of PrEP is to prevent HIV infection even in cases of accidental exposure. Tenofovir and emtricitabine are antiviral drugs that inhibit HIV’s ability to replicate and spread within the human body. A patient at-risk for HIV infection takes PrEP daily to establish a baseline of protection that prevents HIV from gaining a foothold in the body, even if a patient is exposed to the virus.
However, PrEP is not completely foolproof. While PrEP reduces the risk of contracting HIV from sexual activity by 99%, it does not offer any protection against other Sexually Transmitted Diseases (STDs). People using PrEP still need to utilize other methods to protect against STDs, especially regular use of condoms during sexual activity.
For those who inject recreational drugs, PrEP only reduces infection risk by 74% and does not protect against other infections that can be spread by contaminated needles.
Who Should Take PrEP
There are two groups of people PrEP is primarily geared towards. The first are those who are HIV-negative and are either:
in a mutually monogamous relationship with someone who is HIV-positive or are
in a non-mutually monogamous relationship with someone who is HIV-negative but has a history of unprotected sexual activity with high-risk people of unknown HIV status
The term “high-risk” refers to those who inject recreational drugs or have been in/worked in drug treatment programs in the past six months.
People who have a partner who is HIV-positive but are considering getting pregnant can also take PrEP to prevent their baby from becoming infected with HIV.
The CDC has provided online guidance so that those curious about whether PrEP is right for them may identify if they are at risk and whether they should consult their physician.
Developments in PrEP
Other drugs are currently under review as researchers aim to find more effective PrEP drug combinations with fewer side effects.
Marviroc, which prevents HIV from entering and infecting cells, is being tested in combination with other PrEP drugs and as an intravaginal ring for HIV prevention.
A combination of tenofovir alafenamide (TAF) and emtricitabine demonstrated non-inferiority to the Truvada combination, which uses TDF and emtricitabine. It was found that TAF lasted longer in the blood than TDF. While the TAF results are not definitively better than TDF, the findings show promise for longer lasting PrEP medications in the future.
For the time being, PrEP using the TDF and emtricitabine combination remains the approved drug of choice by major public health organizations like the World Health Organization and the US Centers for Disease Control. The move towards generic versions of Truvada, which are expected to become available in September 2020, represent the next biggest hope for patients seeking vital HIV prevention methods without life-inhibiting costs, which can be thousands of dollars.