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Tuesday, July 29, 2025

Pre-Exposure Prophylaxis (PrEP)


Pre-Exposure Prophylaxis (PrEP) is a biomedical HIV prevention strategy that involves the use of antiretroviral medications by individuals who are HIV-negative to reduce their risk of acquiring HIV infection. It is a cornerstone of modern public health efforts to combat the global HIV/AIDS epidemic, particularly among populations at high risk of exposure.

1. Overview and Definition

Pre-Exposure Prophylaxis, abbreviated as PrEP, is a preventive treatment for people who do not have HIV but who are at high risk of being exposed to the virus through sexual contact or injection drug use. When taken consistently, PrEP reduces the risk of HIV infection significantly.

PrEP is not a vaccine, and it does not cure HIV. Instead, it works by maintaining protective levels of antiretroviral drugs in the bloodstream and target tissues, which block HIV from replicating and establishing a permanent infection in the body.

2. Approved Medications for PrEP

There are currently two main medications approved by regulatory authorities such as the U.S. Food and Drug Administration (FDA) for use as PrEP:

a. Truvada

  • Generic Name: Emtricitabine 200 mg + Tenofovir disoproxil fumarate (TDF) 300 mg

  • Form: Oral tablet

  • Use: Daily PrEP for all adults and adolescents (≥35 kg) at risk of HIV

  • Effectiveness: Reduces sexual transmission of HIV by over 99% when taken consistently

b. Descovy

  • Generic Name: Emtricitabine 200 mg + Tenofovir alafenamide (TAF) 25 mg

  • Form: Oral tablet

  • Use: Approved only for men and transgender women who have sex with men; not for people assigned female at birth who are at risk from receptive vaginal sex

  • Advantages: Less impact on bone mineral density and kidney function compared to TDF-based PrEP

c. Apretude (Cabotegravir long-acting injection)

  • Generic Name: Cabotegravir extended-release injectable suspension

  • Form: Intramuscular injection every two months after initial lead-in

  • Use: Approved for adults and adolescents (≥35 kg) who are at risk of HIV via sexual activity

  • Effectiveness: Shown to be even more effective than daily oral PrEP in clinical trials

  • Advantage: Helps those who may struggle with daily adherence to oral medications

3. Indications and Populations for Use

PrEP is recommended for individuals who are HIV-negative but have substantial ongoing risk of HIV exposure. These include:

a. Sexually Active Adults and Adolescents

  • Gay, bisexual, and other men who have sex with men (MSM)

  • Heterosexual men and women with partners of unknown HIV status or known HIV-positive partners not on effective treatment

  • Individuals with recent bacterial sexually transmitted infections (STIs)

  • Individuals who inconsistently use condoms

b. People Who Inject Drugs (PWID)

  • Individuals sharing injection equipment

  • Engaging in risky sexual behavior

c. Serodiscordant Couples

  • One partner is HIV-positive and the other is HIV-negative

  • PrEP is used until the HIV-positive partner is virally suppressed through antiretroviral therapy

d. Sex Workers and Transgender Individuals

  • Recognized globally as high-priority populations for HIV prevention

  • May face barriers to consistent condom use and regular healthcare

4. Mechanism of Action

PrEP medications work by inhibiting reverse transcriptase, an enzyme HIV needs to replicate its genetic material. This action occurs at an early stage in the viral replication cycle, preventing the establishment of infection in HIV-negative individuals upon exposure.

  • Tenofovir (both TDF and TAF) is a nucleotide reverse transcriptase inhibitor (NRTI)

  • Emtricitabine is also an NRTI

  • Cabotegravir is an integrase strand transfer inhibitor (INSTI), blocking integration of viral DNA into the host genome

5. Effectiveness of PrEP

Clinical trials have demonstrated the following reductions in risk of HIV infection:

  • Oral PrEP (Truvada):

    99% reduction in HIV transmission via sexual exposure when taken daily
    ~74% reduction among people who inject drugs

  • Long-acting injectable PrEP (Cabotegravir):
    66% more effective than oral PrEP in men who have sex with men
    89% reduction in incidence compared to oral PrEP among women in a large African trial

Adherence is critical: PrEP is only effective when taken consistently. Missed doses significantly reduce its protective benefits.

6. Initiation and Monitoring

a. Initial Evaluation

Before starting PrEP, healthcare providers should:

  • Confirm HIV-negative status (using fourth-generation antigen/antibody test or nucleic acid test)

  • Assess risk factors and eligibility

  • Screen for STIs, hepatitis B and C, kidney function (for tenofovir-based regimens), and pregnancy (if applicable)

b. Follow-Up Monitoring

  • HIV testing: every 3 months

  • Kidney function tests: every 6 months

  • STI screening: every 3–6 months

  • Adherence and side effect review: every follow-up visit

  • Pregnancy testing (if applicable)

7. Side Effects and Safety

Most people tolerate PrEP well. However, some adverse effects may occur:

a. Common Side Effects

  • Nausea

  • Headache

  • Diarrhea

  • Fatigue

These often resolve within the first few weeks of therapy.

b. Serious or Long-Term Risks

  • TDF (Truvada) may reduce bone mineral density and affect kidney function (requires monitoring)

  • TAF (Descovy) has a more favorable safety profile on bones and kidneys

  • Cabotegravir may cause injection site reactions (pain, swelling, nodules)

8. Drug Interactions

  • PrEP medications have a relatively low potential for drug-drug interactions due to their pharmacokinetics.

  • Tenofovir may interact with nephrotoxic drugs (e.g., NSAIDs, aminoglycosides)

  • Emtricitabine has minimal interaction risk

  • Cabotegravir should be used cautiously with enzyme inducers (e.g., rifampin, carbamazepine) which can lower its effectiveness

Regular medication reconciliation is necessary to minimize potential interactions, especially for those taking multiple medications.

9. Special Populations

a. Adolescents

PrEP is approved for adolescents ≥35 kg. Confidentiality, access, and consent laws vary by jurisdiction.

b. Pregnancy and Breastfeeding

  • PrEP is safe and effective during pregnancy and lactation, particularly for women at high risk of acquiring HIV during these periods.

  • The benefits of preventing HIV outweigh potential risks.

c. Hepatitis B Co-infection

  • Emtricitabine and tenofovir are active against hepatitis B virus (HBV)

  • Stopping PrEP suddenly may lead to hepatitis B flares in co-infected individuals

  • Baseline HBV testing and appropriate vaccination are essential

10. Implementation and Access

a. Global Guidelines

Organizations like the World Health Organization (WHO), CDC, and UNAIDS recommend PrEP as part of comprehensive HIV prevention packages.

b. Access Strategies

  • Available via prescription through healthcare providers

  • Public health programs and NGOs offer PrEP free or at subsidized cost in many countries

  • Online telehealth platforms have expanded access, especially during the COVID-19 pandemic

c. Barriers to Access

  • Stigma and discrimination, especially among key populations (LGBTQ+, sex workers, PWID)

  • Cost and insurance coverage

  • Limited provider awareness and prescribing comfort

  • Structural barriers such as transportation or housing instability

11. Behavioral Considerations and Risk Compensation

A concern raised by some clinicians and policymakers is risk compensation, where individuals on PrEP may engage in riskier behaviors (e.g., reduced condom use), potentially leading to increases in other STIs.

However, evidence shows that:

  • PrEP users generally maintain or improve safer sex practices

  • Routine STI screening within PrEP programs facilitates early detection and treatment of infections

  • PrEP does not protect against other STIs or pregnancy, so condom use is still recommended

12. Adherence Support Strategies

High adherence is essential for maximum protection. Support includes:

  • Education and counseling

  • SMS reminders and mobile apps

  • Pill boxes or blister packs

  • Peer support groups

  • Monthly follow-up visits or telehealth check-ins

  • Long-acting injectable options for those with difficulty adhering to daily pills

13. Future Directions

Research and development continue to expand PrEP options:

  • Topical PrEP: Vaginal rings (e.g., dapivirine ring) with antiretroviral agents

  • On-demand PrEP: Intermittent dosing strategy used around sexual activity (currently only recommended for MSM in certain settings)

  • Implantable devices: Under investigation for long-term drug delivery

  • Broadly neutralizing antibodies (bNAbs): Experimental biologics offering long-term HIV prevention

The goal is to diversify HIV prevention modalities to match individual needs and preferences.

14. Public Health Impact

Since its approval, PrEP has had a significant impact:

  • Decreased new HIV infections in multiple high-income countries

  • Increased engagement in regular HIV/STI testing

  • Empowered individuals to take proactive steps in their sexual health

  • Reduced anxiety about HIV exposure among high-risk individuals

However, disparities in access and uptake remain, particularly in low- and middle-income countries and among marginalized populations.

15. Ethical and Legal Considerations

  • Informed consent is vital before PrEP initiation

  • Confidentiality must be safeguarded, especially in stigmatized groups

  • In many countries, age of consent laws affect adolescent access

  • Medical systems must balance individual autonomy with population-level goals



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