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A Primer on HIV Pre-Exposure Prophylaxis (PrEP)

By: Svetlana Akbasheva, Section Editor (Clinical)

Despite the advances in the treatment of human immunodeficiency virus (HIV), the incidence of HIV transmission remains alarmingly high, with about 50,000 new cases arising every year in the United States alone.1 Recently, HIV management has turned its focus on prevention for high-risk, uninfected individuals in addition to treatment of those with established disease. Currently, the only medication approved for HIV pre-exposure prophylaxis (PrEP) is Truvada®, a once-daily combination pill containing the nucleotide/nucleoside reverse transcriptase inhibitors (NRTIs) tenofovir disoproxil fumarate 300 mg and emtricitabine 200 mg.2,3

The U.S. Public Health Service and Centers for Disease Control and Prevention (CDC) guidelines recommend PrEP for sexually active men who have sex with men, heterosexual men and women, and injection drug users who are at high risk for acquiring HIV. PrEP is also recommended for serodiscordant heterosexual couples, in which only one partner has HIV, as a form of protection if they are trying to conceive a child. However, before any of these patients can receive PrEP therapy, they must be screened for several parameters.2,3

Most importantly, candidates for PrEP must have a negative HIV test, as Truvada® use alone in active HIV infection may be ineffective and breed resistance. In addition, patients must be screened for Hepatitis B infection and receive the vaccine if they have not already done so. Renal function is another baseline screening parameter, as Truvada® is potentially nephrotoxic and should not be used for PrEP in individuals with a creatinine clearance less than 60 ml/min.2,3 Eligible individuals should receive a maximum 90 day supply of medication and need to follow up with their provider every three months for monitoring and counseling.2 An HIV test and a pregnancy test for females needs to be administered during each follow-up visit. Renal function testing is recommended three months after initiating PrEP therapy and then every six months, though more frequent monitoring is advised if a patient has other risk factors for renal impairment such as hypertension, diabetes mellitus, or co-administration of other medications that may affect renal function. Since PrEP does not protect against other sexually transmitted diseases (STDs), patients should be counseled about the importance of using condoms in conjunction with oral PrEP therapy and should be screened for STDs every six months.1,2

Several key studies have demonstrated the efficacy of PrEP in preventing new HIV infections in high-risk patients. The iPrEX study was a randomized controlled trial of PrEP versus placebo in 2499 seronegative men who have sex with men which found that PrEP reduced the incidence of HIV infection by 44% (95% CI, 15% to 63%). When the results were adjusted to include only subjects with detectable drug levels, an indication of adherence to the medication, the relative risk reduction with PrEP therapy became 92% (95% CI, 40% to 99%).4 A second study, called The Partners PrEP study, was a randomized trial of serodiscordant heterosexual couples comparing tenofovir and tenofovir-emtricitabine, respectively, versus placebo for HIV prophylaxis. The results showed that the relative risk reduction for patients on tenofovir-emtricitabine was 75% (95% CI, 55% to 87%), though it jumped to 90% for patients with detectable drug levels in their system.5 Another trial of tenofovir-emtricitabine versus placebo in 1219 HIV-negative heterosexual men and women showed that the combination pill had 62.2% efficacy in preventing HIV infection (95% CI, 21.5% to 83.4%).6 The Bangkok Tenofovir Study focused on the efficacy of tenofovir as PrEP in another high-risk group, injection drug users.7 This randomized, controlled trial found that tenofovir reduced HIV incidence by 48.9% compared to placebo in this population (95% CI, 9.6% to 72.2%).7 In these studies, the rates of serious adverse effects were found to be similar between the active drug and placebo groups, though tenofovir and tenofovir-emtricitabine were found to cause more nausea and decreases in bone mineral density.4,6,7

All of the above studies demonstrated that patients with detectable levels of drug in their system had increased protection against disease acquisition, showing that adherence is key for PrEP efficacy.4-7 Pharmacists can play an important role in HIV prophylaxis by providing PrEP education, monitoring for adverse effects and drug interactions, and counseling patients on the importance of adherence.8 Patients who are worried about the expense of PrEP therapy should be told that many insurance plans cover PrEP and Gilead Sciences offers medication assistance programs for patients without insurance.1 With no cure for HIV on the horizon yet, prophylaxis is fundamental to curbing the HIV epidemic, and the simplicity and proven efficacy of the currently recommended PrEP regimen will hopefully make this an easy pill to swallow.


  1. PrEP. Centers for Disease Control and Prevention. Updated 06/25/2015. Accessed January 01/13/2016.
  2. Preexposure prophylaxis for the prevention of HIV infection in the United States – 2014: a clinical practice guideline. US Public Health Service. Accessed September 15, 2015.
  3. Truvada (emtricitabine/tenofovir disoproxil fumarate) [package insert]. Foster City, CA; Gilead Sciences, Inc.; Revised 10/01/2013.
  4. Grant RM, Lama JR, Anderson PL, et al. Preexposure chemoprophylaxis for HIV prevention in men who have sex with men N Engl J Med. 2010;363(27):2587-99. doi: 10.1056/NEJMoa1011205.
  5. Baeten J, Donnell D, Ndase P et al. Antiretroviral Prophylaxis for HIV Prevention in Heterosexual Men and Women. N Engl J Med. 2012;367(5):399-410. doi:10.1056/nejmoa1108524.
  6. Thigpen MC, Kebaabetswe PM, Paxton LA, et al. Antiretroviral preexposure prophylaxis for heterosexual HIV transmission in Botswana. N Engl J Med. 2012;367(5):423-34. doi: 10.1056/NEJMoa1110711.
  7. Choopanya K, Martin M, Suntharasamai P, et al. Antiretroviral prophylaxis for HIV infection in injecting drug users in Bangkok, Thailand (the Bangkok Tenofovir Study): a randomized, double-blind, placebo-controlled phase 3 trial. The Lancet. 2013;381(9883):2083-2090. doi: 10.1016/S0140-6736(13)61127-7.
  8. Bruno C, Saberi P. Pharmacists as providers of HIV pre-exposure prophylaxis. Int J Clin Pharm. 2012;34(6):803-6. doi: 10.1007/s11096-012-9709-0.
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