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  • Post-exposure prophylaxis (PEP) can prevent HIV infection up to 72 hours after exposure
  • To expedite initiation of PEP, two Toronto clinics prescribed the medication in advance
  • 13% of “PEP-in-pocket” prescriptions were filled, resulting in zero infections

There are several options to reduce a person’s risk of becoming infected with HIV during sex. One option increasingly used in Canada and other high-income countries involves the use of a pill containing two anti-HIV medicines—tenofovir DF and FTC. This pill is sold under the brand name Truvada and also comes in generic formulations. Clinical trials have found that daily use of these drugs, together with other measures, is highly effective at reducing the risk for HIV infection. The use of medicines in this way to prevent HIV infection prior to potential exposure is called pre-exposure prophylaxis (PrEP). Another way to reduce HIV infection is to take PrEP up to 24 hours before and for two days after sex; this is called “on-demand” PrEP.

Yet another biomedical intervention to reduce the chances of becoming infected with HIV after potential exposure during sex or other means is to take a combination of anti-HIV drugs after potential exposure to HIV; this is called post-exposure prophylaxis (PEP). PEP must be initiated as soon as possible and no later than 72 hours after a potential exposure and taken daily for 28 consecutive days.

In Toronto

Doctors at two HIV clinics in Toronto have found that there are some HIV-negative people “who do not meet criteria for daily or on-demand PrEP given their relative infrequency of potential HIV exposures, but who nevertheless remain at risk and are eager to use a biomedical HIV prevention strategy.”

A novel strategy

To help protect this group of people, doctors did something novel: They prescribed PEP in advance, or as they called it, “on-demand,” so that in case of potential exposure patients can initiate PEP on their own and then subsequently seek medical attention. The doctors referred to on-demand PEP as “HIV PEP-in-pocket (PIP).”

The strategy of PIP is designed to prevent HIV while reducing the disadvantages of the traditional way that some people seek and receive PEP. For instance, in the case of potential exposure after business hours or on a weekend or holiday, patients may need to go to a hospital’s emergency department because their doctor’s office may be closed. At the emergency department, they will need to be screened and evaluated for their risk of infection. After this, some people may not receive PEP (particularly if they seek help more than 72 hours after exposure) and some may not choose to wait in busy and sometimes overcrowded emergency rooms.

The Toronto doctors looked back on data that their clinic had collected and found that 30 patients had been prescribed PIP in the past five years. However, only four patients (13%) used PEP during that time. All of them initiated PEP less than 10 hours after a potential exposure and none of them became infected.

Although the small number of people and retrospective design of the Toronto study precludes robust conclusions being drawn about the effectiveness of on-demand PEP, it underscores that perhaps on-demand PEP may be yet another way of helping to prevent HIV infection in a minority of patients. The concept of on-demand PEP is novel and intriguing and should be explored in a prospective clinical trial that focusses on people likely to use it. In theory, PIP offers advantages for protecting people at risk for HIV infection who may not wish to take PrEP either because of infrequent sexual activity or for other reasons.


Post-exposure Prophylaxis (PEP) – CATIE fact sheet

Canadian guidelines on HIV pre-exposure prophylaxis and nonoccupational postexposure prophylaxis – Biomedical HIV Prevention Working Group of the CIHR Canadian HIV Trials Network (CTN)

High rate of mental health issues found among some PEP usersCATIE News

Pre-exposure prophylaxis (PrEP) resources

—Sean R. Hosein


Tumarkin E, Heendeniya A, Murphy P, et al. HIV Post-Exposure Prophylaxis-in-Pocket ("PIP") for individuals with low-frequency, high-risk HIV exposures. Journal of Acquired Immune Deficiency Syndromes. 2018; in press.