Last updated, July 2008

Next due for review, July 2009

If you have had unprotected sex (or shared drug injecting equipment) with somebody you know is HIV-positive, or is from a group at high risk of HIV, such as gay men, then you may be able to get a short course of anti-HIV drugs to try to prevent you becoming infected with HIV.

This is called post exposure prophylaxis, or PEP for short.

Purpose of PEP

PEP has been used for many years for healthcare workers who have had possible exposure to HIV, for example, after accidentally pricking themselves with needles used on people who were known to be HIV-positive or at risk of HIV.

PEP is not a ‘cure’ for HIV. Rather, PEP may prevent HIV from entering cells in the body and so prevent you from becoming infected with HIV. PEP isn’t 100% effective – it is estimated that it works in 80% - 90% instances.

Timing of PEP

To have the best chance of being effective you need to start taking PEP as soon as possible after the possible exposure to HIV. Ideally this should be within 24 hours of the possible exposure, and certainly within 72 hours.

Medicine used for PEP

PEP normally consists of three anti-HIV drugs, from two of the different classes, usually two nucleoside analogues (NRTIs) plus a boosted protease inhibitor.

PEP should be taken for a month, and it is important to take all the doses, at the right time and in the right way.

Where to get PEP

Go to a sexual health clinic. If they operate an appointments system and are fully booked, explain that it’s an emergency and that you need to be seen. If it is a weekend, go to the accident and emergency department, who will contact an HIV specialist who is able to prescribe PEP.

Access to PEP

PEP can be difficult to obtain. Not all clinics are willing to give PEP (although national guidelines now say that they should if there was a risk of HIV transmission) and you may have to go to a number of different hospitals before you find one that is willing to give you PEP. If you live in London where there are many sexual health clinics and HIV treatment centres this may not be too difficult,  if you live anywhere else, it could be much harder.

Where clinics do provide PEP they are unlikely to provide it to everybody who asks for it, but will make their decisions on a case-by-case basis.

They are likely to consider the following:

• Was your partner known to be HIV-positive?
• Was your partner from a group at high-risk of HIV, such as gay men?
• Did the kind of sex you had involve the other person ejaculating in your body (were you passive, receptive, or the ‘bottom’, or were you active, insertive, or the ‘top’?)
• Were you raped?
• Was the sex rough, causing internal trauma or bleeding?
• Where did your partner come from? For example a city like London where there are many people with HIV, or a small town where there is little HIV?
• Would you be able to take PEP for a month?
• Would you be willing and able to return after a month for follow-up tests?

Possible risks of PEP

All anti-HIV drugs can cause side-effects which tend to be worst when you first start taking them, and if you are taking PEP you could experience some unpleasant side-effects such as feeling sick, being sick, diarrhoea, tiredness, and generally feeling unwell.

If you have been exposed to a strain of HIV that is resistant to some anti-HIV drugs then it’s possible that PEP won’t work.

If you are already HIV-positive, but don’t know it, there is a chance of developing drug resistance when you take PEP if you don’t take your doses properly. This could limit your treatment options in the future.

Other things to consider

Do not rely on access to PEP if you are having unprotected sex or sharing drug injecting equipment. Condoms, when used properly, are an effective way of preventing the spread of HIV and most other sexually transmitted infections, and never share needles or injecting equipment.