What Is the Difference Between PrEP and PEP?

Sometimes it’s easier to stop a problem from happening rather than dealing with it after it happens. This concept of prevention is often applied in medicine, where it’s called prophylaxis. 

For example, people who are at high risk of having a stroke due to conditions like underlying heart problems often take blood thinners as prophylaxis. Doing so lowers their risk. Likewise, there’s prophylaxis treatment options for people at high risk for getting certain infections. 

Here, we’ll break down pre-exposure and post-exposure prophylaxis, and talk about some of the infections they can be used to prevent. 

What is pre-exposure prophylaxis (PrEP)?

Pre-exposure prophylaxis is a mouthful. Yet, if we break it down, we know that prophylaxis means prevention. And pre-exposure refers to the time before you’re exposed to something that can cause an infection. This is usually a virus. 

So, pre-exposure prophylaxis means taking action to prevent an infection before you’re exposed to the virus that causes it. Most commonly, this involves taking preventative medications. Pre-exposure prophylaxis may be recommended for people who are at high risk for being exposed to a certain virus. 

Pre-exposure prophylaxis is often referred to as PrEP. You might be familiar with PrEP for HIV prevention, as it’s the most well-known use of PrEP. 

How does PrEP work?

When you take a medication as directed for PrEP, your cells build up a concentration (large amount) of medication. This enables your body to fight off an infection as soon as you’re exposed to a particular virus. 

As mentioned above, timing is key with PrEP. You need to start taking it before potential exposure. It may also take some time after you’ve started taking it to build up high enough levels in your system to be effective. That’s why it’s important to follow your healthcare provider’s instructions for using PrEP.

What is post-exposure prophylaxis (PEP?)

On the other side of exposure, there’s post-exposure prophylaxis (PEP). PEP is an infection prevention method where you’re treated after you’ve potentially been exposed to certain viruses or bacteria. 

This might sound like a typical treatment — like taking antibiotics when you develop a sinus infection. But, it’s a little different. This is because you start PEP treatment before you show any symptoms of an infection.  

Many times PEP is used to prevent viral infections that we don’t have a cure for yet, such as HIV. PEP can also prevent bacterial infections such as tuberculosis and pertussis (whooping cough). Using PEP for these infections can protect the exposed person from severe illness and prevent them from spreading the infection to others. 

How does PEP work?

Bacteria, viruses, and other small germs are all infectants. They use our bodies to grow, multiply, and spread. When you’re exposed to an infectant, it enters your cells so it can make copies of itself. 

Early PEP treatment aims to stop this replication process. It does this by working directly against it or by giving your immune system a boost with extra antibodies to fight it off. Antibodies help your immune system fight an infection and recognize an infectant quickly if you’re exposed to it again in the future.

Similarly to PrEP, the timing of PEP is crucial. You want to start PEP as soon as possible after you’re exposed to a germ. This enables your immune system to attack the germ before it causes a serious or chronic infection. 

What is the difference between PrEP and PEP?

The key differences between PrEP and PEP are timing and treatments. PrEP is started before you’re exposed to the germ and PEP is started after exposure. Treatment options for PrEP and PEP are also different, and they aren’t interchangeable. 

What infections can PrEP and PEP be used to prevent?

PrEP and PEP regimens are probably best-known for HIV prevention. Additionally, HIV is the only infection that has FDA-approved or Centers for Disease Control and Prevention (CDC)-recommended treatment options for both forms of prevention. But there are also PEP options for COVID-19, hepatitis B, and other viral and bacterial infections. More on that later.

PrEP for HIV

FDA-approved medications for HIV PrEP include Truvada and Descovy. Both medications contain HIV antiretrovirals (ARVs) called emtricitabine and tenofovir. Antiretroviral medications help prevent HIV from making copies of itself inside your cells. 

But these medications don’t protect against sexually transmitted infections (STIs). They should be used in addition to safer sex practices (e.g., condoms).

When taken as directed, these medications can lower your risk of getting HIV from sex by 99% and from injection drug use by 74%. These medications should be taken every day. And while they are very good at preventing HIV, Truvada and Descovy alone aren’t approved to treat an active HIV infection. So, it’s important to have frequent HIV testing while on PrEP. 

People who don’t have HIV, but are at a high risk for getting HIV, are good candidates for PrEP. HIV is most often transmitted through sexual intercourse or injection drug use. 

People at high risk for HIV may include those who:

• Have a sexual partner who has HIV  

• Don’t know their partner’s HIV status

• Have multiple sexual partners

• Don’t always use condoms

• Have had a recent STI

• Share injection drug supplies

• Have used PEP multiple times 

For more information on HIV PrEP, check out one of our other articles. 

PEP for HIV

PEP is a good option for people who aren’t taking PrEP and think they might have been exposed to HIV. 

Exposure incidents can include a condom breaking during sex, sexual assault, or an accidental needle stick. Seek medical help right away if you think you might have been exposed to HIV. PEP should be started within 72 hours of the exposure incident, but it’s best to start it as soon as possible. 

The U.S. Public Health Service recommends that PEP contains at least 3 ARVs. Many regimens include emtricitabine and tenofovir, which are the two ARVs used in PrEP. But the difference for PEP is that an additional ARV is added. This is to attack the virus from a different angle. Usually, these ARVs are taken once or twice a day for 28 days. 

Make sure you take your PEP regimen exactly as directed for the full 28 days and follow up with your provider for more monitoring. 

HIV PrEP and PEP both require HIV testing. Your provider will want to confirm your HIV status during your first visit. With PrEP, you usually have HIV testing every 3 months to confirm that you’re still HIV negative. With PEP, you’ll have another HIV test after you finish your 28-day course, and then another one 3 months after the initial exposure. 

COVID-19

Right now, the COVID-19 vaccines — which are not considered PrEP or PEP — are the gold standard for COVID-19 prevention. Yet, there are people who are at a high risk for severe COVID-19 illness and can benefit from prophylaxis treatment.

COVID-19 PEP can prevent severe illness in high-risk people who haven’t been fully vaccinated, or those who’ve been vaccinated but have weaker immune systems. If recommended, PEP should be given as soon as possible after close contact with someone who has COVID-19. 

It’s also recommended for people at high risk for exposure. Examples of this would be people living or working in a setting such as a nursing home or prison where other people have had COVID-19. 

Right now, there are two treatment options authorized for COVID-19 PEP. They are: 

• Bamlanivimab/etesevimab: a one-time infusion into the vein

• Casirivimab/imdevimab (REGEN-COV): infused into the vein or injected under the skin

These medications are monoclonal antibodies. Monoclonal antibodies are lab-made antibodies that target certain proteins. COVID-19 PEP medications work by targeting proteins on the virus that help it infect your cells. These medications work best when they’re given as soon as possible after exposure to COVID-19. But they should be given within 7 days of exposure. 

There are no medications or regimens authorized for COVID-19 PrEP at this time. But clinical trials are studying potential options for PrEP. 

Examples of potential PrEP treatments being researched include:

• Truvada and Descovy (medications used for HIV PrEP)

• Hydroxychloroquine

• Ivermectin

• Monoclonal antibodies

• Supplements

These medications shouldn’t be used as COVID-19 PrEP outside of a clinical trial. 

AstraZeneca has been studying a long-acting antibody combination injection. It’s referred to as “AZD7442” and contains tixagevimab and cilgavimab. AZD7442 has shown promising results in phase 3 trials for COVID PrEP. Because of this, AstraZeneca has submitted an authorization request to the FDA. 

Other infections

In addition to HIV and COVID-19, there are many other infections that can be prevented and contained with PEP. 

Other viral infections that have options for PEP include:

• Hepatitis A

• Hepatitis B

• Rabies

• Varicella zoster (the virus that causes shingles and chickenpox)

Lastly, there’s also PEP for some bacterial infections including:

• Tuberculosis

• Tetanus

• Pertussis

• Serious streptococcal infections 

• Invasive meningococcal disease

• Anthrax

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Written by:

Hope Chang, PharmD, AAHIVP

Hope Chang is a freelance writer and content reviewer for GoodRx. She attended Howard University College of Pharmacy in Washington, D.C. and completed post-graduate residency training at the University of California, Davis Medical Center.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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