4 min read PrEP

PrEP: The Basics

PrEP: The Basics

Introduction

In 2019, over 36,000 people in the United States were newly diagnosed with HIV, the virus that causes AIDs.  The number of new HIV diagnoses was highest among people aged 25 to 34.  Gay, bisexual, and other men who reported male-to-male sexual contact are the population most affected by HIV.  However, men and women who reported heterosexual contact accounted for 23% of the 36,801 new HIV diagnoses. HIV is not just spread through sex; people who inject drugs accounted for 7% of the new HIV diagnoses.

There are over 1,189,700 people living with HIV in the the United States; 1 out of 7 people infected with HIV do not know they have it.  Pre-exposure prophylaxis (PrEP) using antiviral medications is an effective way to prevent new HIV infections in those at greatest risk.

What is PrEP

PrEP is the use of combination antiretroviral therapy in a single pill to prevent HIV infection.  Tenofovir disoproxil fumarate 300 mg-emtricitabine 200 mg (TDF-FTC) is the most widely studied regimen and it can reduce the risk of HIV transmission by close to 100% when taken daily as prescribed.

How does PrEP Work?

Tenofovir disoproxil is a nucleotide analog reverse-transcriptase inhibitor and emtricitabine is a nucleoside reverse-transcriptase inhibitor - both medications work by inhibiting HIV reverse transcriptase, a crucial enzyme that is necessary for HIV viral replication.  Taken once a day, it can prevent up to 99% sexually transmitted HIV.

Who is PrEP for?

Lot's of people. PrEP is recommended for sexually-active MSM (men who have sex with men) and transgender women who have sex with men at substantial risk(1) of HIV acquisition:

  • HIV-positive sexual partner
  • Recent bacterial STI (sexually transmitted infection)
  • Multiple sex partners
  • History of inconsistent or no condom use
  • Commercial sex work

PrEP is recommended for adult heterosexual cisgender(2) men at substantial risk of HIV acquisition:

  • HIV-positive sexual partner
  • Recent bacterial STI (sexually transmitted infection)
  • Multiple sex partners
  • History of inconsistent or no condom use
  • Commercial sex work
  • In a high HIV prevalence area or network

PrEP is recommended for adult heterosexual cisgender women and transgender men at substantial risk of HIV acquisition:

  • HIV-positive sexual partner
  • Recent bacterial STI (sexually transmitted infection)
  • Multiple sex partners
  • History of inconsistent or no condom use
  • Commercial sex work
  • In a high HIV prevalence area or network

PrEP is recommended for adults who inject drugs at substantial risk of HIV acquisition:

  • HIV-positive injecting partner
  • Sharing injection equipment

Clinical Eligibility

Documented negative HIV test result and no signs/symptoms of acute HIV infection within the last 4 weeks.

We want to prevent drug resistant virus Everyone with HIV should be treated with a combination antiretroviral regimen that usually consists of three antiretroviral medications, and the use of TDF-FTC for PrEP would put HIV-infected individuals at risk for developing drug-resistant HIV.

Seroconversion takes time Acute HIV infection may present as a viral syndrome (eg, enlarged lymph nodes, fever, malaise, and/or a rash) and have detectable HIV RNA but not HIV antibody in early cases.  Seroconversion - the development of detectable antibodies against HIV infections - takes time to detect; we use industry-leading fourth generation enzyme linked immunoassays that can detect evidence of HIV infection - IgM and IgG antibody and p24 antigen - approximately 15 to 20 days after infection.

Kidney function evaluation

Premium non nocere. Individuals with a creatinine clearance of less than 60 ml/min/1.72^2 should not use TDF-FTC since it can cause kidney injury including acute renal failure and Fanconi Syndrome.(3)  We monitor kidney function and HIV status every three months for everyone on PrEP.

Hepatitis B Screening

Individuals with no serologic evidence or prior HBV infection or vaccination should be vaccinated against HBV since they’re at risk of acquiring HBV. For individuals with evidence of chronic HBV infection, TDF and TAF are potential first-line treatments and thus can be used as a PrEP regimen and used to treat HBV.  In individuals who do not require treatment for chronic HBV, there’s a theoretical risk that discontinuing PrEP may cause a flare up of their HBV.

Osteoporosis

TDF has been associated with a reductions in bone density.(4)  There are no proven strategies to prevent potential bone loss in patients taking PrEP.  One study showed that vitamin D3 plus calcium supplementation mitigated bone loss in patient with HIV taking a TDF-based antiretroviral regimen.(5)  We recommend maintaining adequate vitamin D levels, although specific studies evaluating this recommendation are currently ongoing.

Screening for pregnancy in women of childbearing potential.

The use of TDF and emtricitabine (both pregnancy category B drugs)(6) during pregnancy, although thought to be safe, raises concerns about fetal bone development.  For those who are pregnant, the risk of acquiring HIV must be weight against the risk of using antiviral medications during pregnancy and the limited date on the efficacy of PrEP during pregnancy.

Medication Adherence

When taking PrEP, it’s very important to take the medication daily as prescribed.  There is a clear association between taking the drug daily and its ability to prevent HIV transmission.

Condom Use

PrEP does not protect against other sexually transmitted infections (STI).  Wear condoms whenever possible to reduce the risk of acquiring other STIs like syphilis and hepatitis C as well as to prevent unwanted pregnancy.

When starting PrEP, condoms should be worn if engaging in sexual activity until adequate drug concentrations that protect against HIV can form.  For people engaging in receptive anal sex, PrEP provides protection after day seven of continual use.  For people engaging in receptive vaginal sex, PrEP takes twenty-one days to provide protection,


References

  1. any of the following within the last six months
  2. https://genderspectrum.org/articles/understanding-gender
  3. Product Information: TRUVADA(R) oral tablets, emtricitabine tenofovir disoproxil fumarate oral tablets. Gilead Sciences Inc (per FDA), Foster City, CA, 2017
  4. https://pubmed.ncbi.nlm.nih.gov/25908682/
  5. https://pubmed.ncbi.nlm.nih.gov/26075752/
  6. https://chemm.hhs.gov/pregnancycategories.htm