Pre-Exposure Prophylaxis and HIV Prevention

Overview of HIV/AIDS and Its Impact

HIV/AIDS remains a global pandemic, presenting significant challenges to healthcare systems worldwide. In Canada, the estimated incidence of HIV infection in 2014 was approximately 2,570 new cases, a slight decrease from the 2,800 reported in 2011. Continuous efforts are essential to prevent a resurgence of this disease.

Role of Pre-Exposure Prophylaxis

The World Health Organization advocates for pre-exposure prophylaxis (PrEP) utilizing antiretroviral medications to significantly lower the risk of HIV infection in HIV-negative individuals at high risk. Research has established that daily oral PrEP, specifically the combination of tenofovir disoproxil fumarate and emtricitabine (known as Truvada), is effective in preventing HIV infection among various high-risk groups, including men who have sex with men, intravenous drug users, heterosexual men and women, and HIV-negative partners in serodiscordant relationships.

On-Demand PrEP: ANRS IPERGAY Trial Findings

A notable randomized control trial, the ANRS IPERGAY trial, conducted across multiple sites in France and Quebec, Canada, demonstrated that on-demand use of emtricitabine/tenofovir before and after sexual activity resulted in an 86% reduction in HIV infection risk among men who have sex with men compared to a control group. Although this trial was halted prematurely, the same research team initiated an open-label study involving participants from the original trial and additional high-risk individuals.

Eligibility and Study Design

Participants in the follow-up study were required to be at least 18 years old, hepatitis B-negative, and have normal kidney and liver function. A total of 361 participants enrolled in this trial. They received a regimen of 300 mg of tenofovir disoproxil fumarate and 200 mg of emtricitabine per pill, with specific instructions to take two pills 2-24 hours before sex, one pill 24 hours after, and another pill 24 hours later. For multiple sexual encounters, participants were instructed to continue taking one pill daily until the last sexual encounter, followed by two additional pills.

Monitoring and Results

Participants underwent regular testing for HIV, syphilis, gonorrhea, and chlamydial infections, and were counseled to ensure adherence to the prophylactic regimen. The median follow-up period was 18.4 months. While 63 participants discontinued early and one individual contracted HIV during follow-up—having ceased PrEP early—the study noted an increase in condomless receptive anal sex from 77% at baseline to 86% at 18 months. Additionally, 43% of participants acquired at least one bacterial sexually transmitted infection during the follow-up, consistent with rates observed in the original trial.

Conclusions on PrEP Effectiveness

The findings from this trial reinforce that using antiretroviral drugs for pre-exposure prophylaxis is highly effective in lowering the risk of HIV infection within high-risk populations. The incidence rate of HIV among those receiving on-demand PrEP was 97% lower compared to the control group in the earlier trial. Although condoms have traditionally been the most effective method for preventing HIV transmission, the efficacy of PrEP in reducing infection risk among intravenous drug users is a promising development. Future research may explore the effectiveness of on-demand PrEP in additional high-risk groups, including heterosexual men and women.

Author Information

Written by Usha B. Nair, Ph.D.