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Pre-exposure Prophylactic Medicine for Human Immunodeficiency Virus May Be Effective in Curbing the Spread of the Virus

Last updated Sept. 10, 2015

Approved by: Maulik P. Purohit MD MPH

Kiran Foster

"What our study shows very reassuringly is that PrEP works in a real world setting. HIV prevention in 2015 is very exciting because we have several tools that are available for reducing risk, and PrEP is one of those tools."


The US Food and Drug Administration approved a drug for Human Immunodeficiency Virus (HIV)-negative individuals in 2013. The drug, a combination of Emtricitabine and Tenofovir, was shown in clinical studies to reduce the risk of an HIV-negative person getting infected by the virus significantly, even when one partner in the relationship was HIV-positive. The medication is available in a pill form and is considered Pre-Exposure Prophylaxis or PrEP, which prevents high risk, HIV-negative individuals from getting infected with the virus. The two requirements for the drug to work effectively were that
  • The individual must be HIV-negative and at substantial risk of getting infected.
  • The pill needs to be taken daily.

A new study conducted at Kaiser Permanente San Francisco Medical Center has further investigated the efficiency of the drug in a high-risk population. In an investigation that ran for a total duration 32 months, 657 individuals volunteered, the majority being homosexual men who had sex with other men. The study subjects were prescribed PrEP for daily use, once a day.  

The participants were checked for baseline HIV as well as other sexually transmitted infections (STIs) at the beginning of the study and every three months thereafter, till end of the study period. A survey was also conducted to ascertain sexual behavior of the study subjects.

The results of the study were as follow:

  • PrEP was successful in preventing HIV infection in 100% of participants.
  • All participants remained HIV-free at the end of the study period.
  • Although HIV infection was prevented, other STIs increased in the study participants.
  • At the end of 6 months of PrEP use, 30% of study participants had at least one STI (chlamydia, gonorrhea, syphilis, etc.)
  • At the end of one year of PrEP use, 50% of participants had at least one STI.
  • 74% of the 143 participants who responded to a survey (at the end of 6 months) regarding sexual behavior reported not changing the number of sexual partners; 11% of the respondents reported an increase in the number of sexual partners and 15% reported a decrease.
  • 41% of the responders reported decreasing condom use. Condom use was unchanged in 56% and increased in 3% of respondents. 

The lead author of the study, Dr. Jonathan Volk, says (as reported by Huffington Post), "What our study shows very reassuringly is that PrEP works in a real world setting. HIV prevention in 2015 is very exciting because we have several tools that are available for reducing risk, and PrEP is one of those tools." 

Although the study is promising and reiterates earlier findings on PrEP, it also raises several questions. Some of them are:

  • Will the majority of individuals in the high-risk population be able to afford this medication?
  • Will the medication be taken as prescribed?
  • Is there a correlation between the increase in other STIs with the use of PrEP (as observed in the study)? Since the study did not involve controls (people on placebo or without PrEP), it is difficult to conclude if there exists a correlation. The fact that the study was conducted in a high-risk population is noteworthy. As the authors state in the article, "...ongoing screening and treatment for STIs, including hepatitis C, remain an essential component of PrEP delivery." 
  • Does PrEP need to be taken with additional medication to curb other STIs?
  • Because use of PrEP resulted in decreased use of condoms in the study population, will PrEP encourage risky behavior in the high-risk population?
  • What are the side effects of prolonged use of PrEP?

Ongoing clinical trials to test the efficacy of PrEP in heterosexual individuals, in women and young adults should provide answers for many questions. In the mean time, the findings of this study are reassuring, to say the least.

Written by Mangala Sarkar, Ph.D.

Primary References

Volk, J., Marcus, J., Phengrasamy, T., Blechinger, D., Nguyen, D., Follansbee, S., & Hare, C. (2015). No New HIV Infections with Increasing Use of HIV Preexposure Prophylaxis in a Clinical Practice Setting. Clinical Infectious Diseases. doi: 10.1093/cid/civ778

Truvada Protected 100 Percent Of Study Participants From HIV. (n.d.). Retrieved September 8, 2015, from http://www.huffingtonpost.com/entry/truvada-protected-study-participants-from-hiv_55e9f596e4b002d5c07607a5

Additional References

FDA Approves First Medication to Reduce HIV Risk. (n.d.). Retrieved September 8, 2015, from http://www.fda.gov/forconsumers/consumerupdates/ucm311821.htm

(2015, August 26). Retrieved September 8, 2015, from http://www.cdc.gov/hiv/prevention/research/prep/index.html

Search Results. (n.d.). Retrieved September 8, 2015, from https://www.clinicaltrials.gov/ct2/results?term=Truvada&Search=Search

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Sept. 10, 2015
Last updated: Sept. 10, 2015