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  • Some HIV drugs taken within 72 hours of a potential exposure reduce the risk of infection
  • Researchers in Boston tested the HIV medication Biktarvy as post-exposure prophylaxis (PEP)
  • The study found Biktarvy was well tolerated as PEP with no HIV transmissions

HIV post-exposure prophylaxis (PEP) is an important part of several HIV prevention options. Studies with monkeys have found that a combination of antiviral drugs reduces the risk of infection with simian immunodeficiency virus (SIV) if given within 72 hours of exposure to this virus. SIV is closely related to HIV. Guidelines for PEP in people recommend that PEP be initiated as soon as possible after potential exposure to HIV, to a maximum of 72 hours.

There have not been large randomized controlled trials of different regimens for PEP. Instead, researchers opt for non-randomized studies.

In Boston

Fenway Health is a long-standing clinic and research centre serving the LGBT community in Boston. Researchers at the centre conducted a study of PEP using a pill called Biktarvy. This pill is taken once daily and contains three medications:

  • bictegravir – 50 mg
  • TAF (tenofovir alafenamide) – 25 mg
  • FTC (emtricitabine) – 200 mg

Biktarvy is widely used in Canada and other high-income countries as a treatment for HIV. It is highly effective and generally well tolerated.

Researchers in Boston enrolled 52 adults who had very recent exposure to HIV and who sought PEP. All participants were briefly interviewed by a doctor or nurse and underwent an HIV rapid test. The rapid test would have screened for current HIV infection by detecting antibodies due to an infection that occurred much earlier than in the past 72 hours. (This is because the immune system would not have had time to produce antibodies if it had been exposed to HIV in the past 72 hours.) People who tested positive with the rapid test would have been swiftly referred for HIV care.

Participants who were HIV negative were offered a supply of Biktarvy, taken for 28 consecutive days.

All but one participant completed the study. Testing up to two months after participants first entered the study found that all were HIV negative. Side effects from Biktarvy were generally mild and not common.

The researchers reviewed other data from what they called “historical” studies of PEP regimens and made comparisons with the current study. They concluded that Biktarvy was better tolerated than older PEP regimens.

Study details

Researchers recruited participants who may have been exposed to HIV through condomless intercourse. Participants were referred through the following means:

  • primary care providers
  • a hotline in an HIV treatment and prevention clinic
  • self-referrals after an online and in-person community educational campaign

At the initial study visit, blood samples were drawn for additional HIV tests, screening for hepatitis B virus (HBV) infection, and to assess the health of the liver and kidneys. PEP was provided in advance of receiving the results of those blood tests. People who tested negative for HBV were offered vaccination against this virus.

Participants who developed any bothersome side effects were encouraged to contact study staff to discuss them. Participants returned to the clinic two weeks after their initial visit and again four weeks after the initial visit. Three months after first visiting the clinic, participants were offered HIV testing.

At the end of the study, researchers compared data from other studies on PEP using regimens such as the following:

  • AZT + a protease inhibitor
  • raltegravir (Isentress) + TDF + FTC
  • Genvoya – a pill containing elvitegravir + cobicistat + TDF + FTC

Participants entered the study between August 2018 and March 2020.

The average profile of participants was as follows:

  • age – 37 years (range: 21 to 71 years)
  • 49 men, 2 women and 1 transgender man; most men were gay or bisexual
  • major ethno-racial groups: White – 77%; multiracial – 12%; Hispanic – 12% (percentages do not total 100 due to overlap)
  • 56% of participants disclosed more than one recent potential exposure to HIV

Side effects

Common side effects were as follows:

  • nausea or vomiting – 15%
  • fatigue – 10%
  • diarrhea or loose stools – 8%

These symptoms were usually mild and temporary. However, one person left the study prematurely because of excessive fatigue.

Completed the 28-day course of PEP

According to the researchers, 90% of participants completed the 28-day course of PEP. The remaining 10% of participants stopped contact with the clinic.

Bear in mind

The results of the present study are encouraging. Hopefully, a larger study with a more diverse population will confirm the findings. The researchers also noted that other studies have found that the following combinations are safe and effective for HIV PEP:

  • dolutegravir (Tivicay) with TDF + 3TC
  • dolutegravir with TDF + FTC

However, they also noted that such regimens would involve taking two pills daily.

Note that PEP is meant as an emergency measure. For people with ongoing exposures to HIV, discussion with a healthcare provider about options to minimize the risk of HIV infection, including the use of HIV pre-exposure prophylaxis (PrEP), is a prudent course of action.

Biktarvy blister packaging approved in Canada

In other developments, Health Canada has approved blister packaging for Biktarvy. This can make it easier for patients to keep track of doses that they have taken.

—Sean R. Hosein


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Canadian guideline on HIV pre-exposure prophylaxis and nonoccupational postexposure prophylaxis CMAJ


  1. Mayer KH, Gelman M, Holmes J, et al. Safety and tolerability of once-daily co-formulated bictegravir, emtricitabine, and tenofovir alafenamide for post-exposure prophylaxis after sexual exposure. JAIDS. 2022; in press.
  2. Irvine C, Egan KJ, Shubber Z, et al. Efficacy of HIV postexposure prophylaxis: Systematic review and meta-analysis of nonhuman primate studies. Clinical Infectious Diseases. 2015 Jun 1;60 Supplement 3:S165-9. 
  3. Health Canada. Supplement to a new drug submission: Biktarvy. Notice of Compliance. 2 November 2021.