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A guide to – PEP
(Post-exposure prophylaxis for HIV)

PEP - the basics 
‘Post-exposure prophylaxis’ (PEP) is a course of medication for 28 days to try and prevent you getting HIV after a recent risk of exposure to the virus. It is important to start PEP as soon as you can after a possible exposure (ideally within 24 hours although PEP can be given up to 72 hours after an exposure). 

PEP is used in the following circumstances:
•	Sexual exposure: PEP may be given after condomless sex with someone who is living with HIV (and is not on effective treatment*) or thought possibly to be living with HIV. Condomless sex means sex without a condom, or sex with a condom which breaks or comes off during sex. 

You may also be offered PEP in a few other circumstances such as:
•	Occupational exposure: following needle-stick injury or splash injury from someone living with HIV (and not on effective HIV treatment). The risk is usually very low. If you are prescribed PEP because of a potential exposure to HIV at work, it is important that you contact your occupational health department as soon as possible to inform them that this has happened.
•	People who inject drugs: sharing injecting equipment with a person living with HIV (and not on effective HIV treatment) or in an HIV outbreak situation (an increase number of HIV cases in local area).
•	Following a sexual assault or rape: a risk assessment will be carried out and PEP offered if it is recommended.
•	Missed PrEP doses: tell the doctor or nurse if you have missed some PrEP (Pre-exposure prophylaxis) doses before your most recent sexual contact as you may need to switch to PEP (post-exposure prophylaxis).
* A person living with HIV on effective treatment and an undetectable viral load cannot transmit HIV to sexual partners.

What is HIV? 
HIV stands for ‘human immunodeficiency virus.’ HIV can damage a person’s immune system and put them at risk of a range of serious illnesses if left untreated. In the 1980s, before HIV was identified, these illnesses were grouped together under the label of the acquired immunodeficiency syndrome (AIDS).

Nowadays in the UK, very few people develop AIDS because their HIV is diagnosed promptly and controlled by highly effective HIV treatment. Thanks to HIV treatment, people living with HIV can enjoy good health and live a normal lifespan. HIV treatment has to be taken for life.  
What is PEP? 
Post-exposure prophylaxis (PEP) is a course of medication for 28 days to try and prevent you getting HIV after a recent risk of exposure to the virus. It is taken in emergency situations as soon as possible after an exposure (ideally within 24 hours although PEP can be given up to 72 hours). 
Although PEP can be very useful in emergency situations this is not the most effective method of HIV prevention. More effective prevention methods include using condoms during sex, taking PrEP, regular HIV testing and immediate treatment of people living with HIV.
PrEP (pre-exposure prophylaxis) is a highly effective HIV prevention strategy. It is different to PEP (post-exposure prophylaxis) as it involves taking medication before sex (either every day or event-based dosing). Please ask your sexual health clinic about PrEP.

Where can I get PEP? 
You can get PEP from sexual health clinics or emergency departments (also known as ‘A&E’). It is important that you tell the clinic staff that you think you may need PEP. They will make sure that you are seen as soon as possible. After a sexual exposure, if the sexual health clinic is closed, you should go to your nearest emergency department (ED). Large ED units are open 24/7. 

It is important for you to know that PEP is not always needed. Health professionals use the British Association for Sexual Health and HIV (BASHH) guidelines to decide who needs to take PEP.

How soon should I start PEP? 
As soon as possible, because the sooner the treatment is taken, the better it works, ideally within the first 24 hours. However, PEP can offer protection if it is started up to 72 hours after a risk has happened.

How long do I need to take PEP?
PEP needs to be taken for 28 days. It is essential to take the full course of treatment to get the full benefit from it. You may have been given a starter pack with a 3 to 5-day course of medication (rather than the whole 28-day course). If you have been given a starter pack, it is essential that you get the full 28-day course from a sexual health clinic, BEFORE the starter pack runs out.
What medicines are in PEP? 
PEP in the UK is usually a combination of a tablet called raltegravir and a tablet called tenofovir/emtricitabine. Some countries use different medication as PEP. In certain situations, your doctor may give you treatment other than raltegravir and tenofovir/emtricitabine.

How do I take PEP?
If TV in pregnancy is not treated, there is an increased risk of labour starting early and the baby being delivered prematurely, or the baby having a low birth weight. At the moment we do not know if treating TV during pregnancy will stop these complications from happening. 
The tests and treatment are the same in pregnancy. Your doctor will discuss things in more detail with you. 

How common is TV? 
Start the medication as soon as you receive it:
Raltegravir*: TWO (600mg) tablets every 24 hours (i.e. two tablets once daily)
Tenofovir/emtricitabine ONE tablet every 24 hours (i.e. one tablet once daily)

*In certain situations such as use of a 3-5 day starter pack, pregnancy or drug interactions you may be asked to take Raltegravir (400mg) twice daily instead. 

Does PEP have any side effects?
PEP is usually safe and most people who take it will have no side effects. However, like all medicines, raltegravir and tenofovir/emtricitabine can sometimes cause unwanted symptoms. Commonly reported problems (up to 1 in 10 patients) include feeling sick, a lack of energy, dizziness, diarrhoea (loose or watery bowel motions), loss of appetite, trouble sleeping, headache and stomach ache. If any of these problems happen, they are usually mild and don’t last very long. However, if the side effects are causing a big problem for you or making it difficult for you to carry on taking PEP you should phone the sexual health clinic and ask for advice before you decide to stop taking PEP.

If you get a skin rash or flu-like illness while taking PEP this might be because you have developed an allergic reaction to the medication. However, the same symptoms sometimes happen after HIV infection.  So, if you develop a skin rash or a flu-like illness while taking PEP or in the 6 weeks after finishing PEP, you should contact the clinic as soon as possible.

What tests do I need?
It is important to have an HIV test when you start taking PEP to make sure you don’t already have HIV. Very rarely, PEP can cause liver or kidney damage so blood tests to check your liver and kidneys are taken as a precaution when you start PEP. You may be advised to have tests for sexually transmitted infections (STI) such as chlamydia, gonorrhoea and syphilis.  The clinic may offer you a course of injections to protect your liver from infection with hepatitis B and A virus which, like HIV, can be transmitted during sex.

Does PEP work?
The risk of getting HIV from a single sex act with a person living with HIV and not taking effective antiretroviral medication is very small (<0.01-1.5% depending on the type of sex). Research shows that acquiring HIV is much less likely if you take PEP. However, PEP does not work every time and some people may still get HIV despite taking PEP. It is important that you do not miss any tablets. You may wish to put an alarm on your phone to help remind you to take your medication. PEP is less likely to work if you miss tablets or if you don’t complete the full 28-day course.

What do I do if I miss my dose or forget to take PEP?
•	If you forget to take a dose, take it as soon as you remember it.
•	However, if it is time for your next dose, skip the missed dose and go back to your regular schedule.
•	Do not take a double dose to make up for a forgotten dose.
•	If more than 48 hours has elapsed since the last dose then contact your clinic asap. 

Can I take PEP if I am pregnant?	
Yes, raltegravir and tenofovir/emtricitabine can be taken in pregnancy. You will be asked to use raltegravir twice daily (400mg) instead of once daily. Both medications are unlicensed in pregnancy so it is important to tell the doctor if you are pregnant or breastfeeding. The doctor will discuss the benefits and risks of PEP with you.
What should I do if I am taking other medication?	
It is very important to tell the doctor or clinician about any other medication you are taking or plan to take during the 28-day PEP course, this includes over-the-counter medicines and herbal preparations. The doctor can then check that these won’t stop your PEP from working. 

Some indigestion treatments (such as antacids containing aluminium, magnesium or calcium) and supplements (including calcium, iron, magnesium or multivitamins) can interfere with PEP so should be avoided whilst on once daily raltegravir. If these medications cannot be avoided then please speak to your clinician for advice. 

Can I have sex while taking PEP?
If you have sex while taking PEP, we advise you to use condoms every time, until your clinic confirms that you are not at risk of passing HIV on to another person. This is particularly important as people who have recently acquired HIV can have a very high viral load (amount of HIV virus in the blood stream) which increases the risk of passing HIV to another person. The final HIV test usually happens no earlier than 11 weeks after the risk. You can ask for free condoms from the clinic. 

Who can support me through this time?
Doctors, nurses and health advisers in the sexual health clinic are there to support you. They can also put you in touch with support groups, helplines, charities and organisations in the community. If you feel able to talk to friends or family during this time you may find it very helpful.

What happens after I finish PEP?
The clinic will advise you to have an HIV test 11 weeks after the risk to make sure that the PEP has been effective. You may also be advised to test for syphilis and hepatitis C infection. If there is likely to be on-going risk of getting HIV, you may be offered PrEP (taking HIV medication before sex).

This leaflet was produced by the Clinical Effectiveness Group of the British Association for Sexual Health and HIV (BASHH). The information in the leaflet is based on the United Kingdom BASHH national guideline for the use of HIV post-exposure prophylaxis 2021’ published by BASHH. 

More information: BASHH: 

The leaflet was developed following The Information Standard principles developed by NHS England. 

More information:

If you would like to comment on this leaflet, e-mail us at: [email protected]. Please type ‘PEP PIL’ in the subject box.

Copyright BASHH 2022. This leaflet was first published in 01/2018 and updated in 10/2022. Review date 2027.