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Post Exposure Prophylaxis

Estimated reading time: 5 minutes

Picture the scene

You are on a busy shift in ED when a young man in his twenties presents after having being triaged with a “personal problem” he would not disclose in triage. He has asked to see a senior doctor urgently.

When alone, he discloses unprotected oral intercourse two days ago in a local sauna for gay men. He was the recipient and there was no ejaculation involved. The details of the sexual practice itself baffle you and the patient is requesting PEPSE (post-exposure prophylaxis following sexual exposure). ou scratch your head, as the area you work in is known to have a low HIV prevalence and you are unsure if the described rather unusual sexual intercourse is in itself an indication to start PEPSE.

Post exposure guidance

The British Association for Sexual Health and HIV (BASHH) in the UK have recently revised its guideline on who should receive PEPSE following sexual exposure. The guideline is based upon a comprehensive review of the literature and the recommendations are based upon a combination of biological plausibility, cohort studies, data from PEP in other settings and expert opinion.

This is clearly a crucial decision for the patient presenting to ED at 2am and potentially a difficult one for the EP if not aware of the guidelines or the local prevalence of HIV in his/her area of practice.

What is the risk?

The risk of an individual acquiring HIV following an exposure is dependent upon the risk that the source is HIV- positive where unknown and the risk of infection following a specific exposure from an HIV-positive individual: The risk of HIV transmission can therefore be calculated.

Risk of transmission = risk that source is HIV-positive X risk of exposure

Knowledge of local HIV prevalence rates will clearly assist in calculating the risk of transmission and cumulative risk should be considered for repeated exposures.

It is worth mentioning that the probability of HIV transmission depends upon the exposure characteristics (anal, oral or other types of sexual practice), the infectivity of the source (viral load) and host susceptibility (immunosuppression). Some factors increase the risk of transmission like the presence of ejaculation, the presence of genital ulceration, the viral load, the absence of circumcision etc.

Post exposure prophylaxis (PEP) is not 100% effective and individuals have acquired HIV despite commencing PEP following both occupational and sexual exposures. Delayed initiation of PEP, presence of resistant virus in the source, different penetration of drugs into tissue compartments, poor/non-adherence and further high-risk sexual exposures may explain some transmissions.

Adherence and completion rates to the recommended four weeks of PEP among health-care workers and individuals exposed non-occupationally have been historically poor for several reasons.

There have also been concerns that the availability of PEPSE will reduce commitment to primary prevention strategies (the use of condoms) and consequently result in more frequent high-risk behaviour. Emergency physicians must perform a risk versus benefit analysis for every individual presenting following an exposure and the decision to initiate PEP is made on a case-by-case basis. This should consider both the risk of transmission according to exposure and the risk of the source being HIV-positive as well as the viral load in the source if known (this is clearly difficult to ascertain in most of ED cases).

When should you prescribe PEP?

The writing committee recommends that PEPSE is indicated when the estimated transmission risk is 1 in 1000 or greater.
The same committee also feels that when the exposure is classified as ‘consider’, PEPSE should only be prescribed if there are additional factors that may increase the likelihood of transmission, i.e. following sexual assault, in the presence of an STI (i.e. where the source is known to have an STI or the exposed individual has symptoms or signs suggesting an STI) or where the source is suspected to have acute HIV infection.

Given that, for optimal efficacy, PEPSE should be commenced as soon as possible after exposure, 24-hour access has now been made be available nationwide in the UK.

Emergency physicians therefore assume significant responsibility for the provision of PEPSE, with the need for support and training from areas of local expertise.

It is recommended that individuals presenting for PEPSE should be referred and seen as early as possible by a clinician or team experienced in the management of PEPSE and with expertise in HIV testing and transmission – whether or not PEPSE is offered or accepted.

Take home message

  •  familiarise yourself with your national/local protocol for PEPSE (it is not difficult with 24h internet access)
  • know your local HIV prevalence (get yourself bleeped out of the consult room by your nurse and google it)
  • a systematic and professional approach in the often sensitive details of sexual practice is essential (who knows, you might come across something you could put into practice at home with your partner!)
  • ask for specialist help if in any doubt (pick up that phone and call a friend!)

Cite this article as: Janos Baombe, "Post Exposure Prophylaxis," in St.Emlyn's, July 1, 2012,

4 thoughts on “Post Exposure Prophylaxis”

  1. Great post Janos, deserves a wide read and reflection. I’m seeing plenty of patients come to ED asking about PEPSE so this is really helpful.

    It’s a bit off topic, but what do you think about offering HIV screening in the ED?



  2. Kirsten Walthall

    We did CT2 teaching on HIV, PEP and screening a couple of weeks ago – had forgotten about this post Janos – will recommend it as essential reading :0)

    We discussed screening (naturally summarising by looking at CEMs best practice position statement on the topic). Interestingly the majority of the group felt that screening should not be offered by EPs, but if offered in the ED (high prevalence areas only) that consent, testing and follow up should be offered by a completely separate team as a distinct package.


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  4. Pingback: PEP, PrEP and all things HIV. St Emlyn's • St Emlyn's

Thanks so much for following. Viva la #FOAMed

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