From TreatmentUpdate 152 Study finds PEP not 100% effective in preventing HIV infection Some doctors and nurses who care for PHAs may sustain needle-stick injuries. This raises the possibility that they may develop HIV infection. To prevent this, a number of studies have been conducted in which health care workers exposed to HIV have received anti-hiv drugs for four weeks. For instance, in the 1990s, researchers found that giving AZT to health care workers who were exposed to HIV was able to prevent HIV transmission in about 81% of cases. Taking anti-hiv drugs to prevent this form of transmission is called PEP, or post-exposure prophylaxis. In studies with monkeys, treatment within 72 hours of exposure to SIV (Simian Immunodeficiency Virus, which causes AIDS in those animals) reduces their risk of infection. Based on this and other results, researchers in San Francisco conducted a study about the ability of PEP to prevent sexual and needle-use transmission of HIV in people. In analyzing data from 702 participants who were given PEP within 72 hours of exposure, they found that most were protected from developing HIV infection. It is important to note that PEP did not provide 100% protection in cases of sexual exposure. Why this might have happened is explored in the report below. Study details Researchers in San Francisco conducted two studies of PEP and combined the data they collected for this analysis. In both studies, participants received PEP within 72 hours of possible exposure to HIV. Some participants received two counseling sessions, while others received up to five counseling sessions, focusing on reducing the risk of transmitting HIV, along with other messages, including adherence to PEP. Routes of infection Eligible participants had to have engaged in sex without condoms as follows: receptive or insertive anal intercourse unprotected vaginal intercourse receptive oral intercourse with ejaculation Also, certain other potential routes of exposure were considered, including: sharing of needles for street drug use contact with a potentially infectious body fluid on a mucosal membrane or skin that was damaged because of a cut, scrape or abrasion The potential exposure must have occurred with a partner who had one of the following characteristics: HIV infection was a man who had sex with another man injected street drugs engaged in sex work was an anonymous sexual partner Participants who entered the study were given the following therapies: AZT coformulated with 3TC (Combivir) d4t and 3TC d4t and ddi
Whenever possible, researchers also interviewed the person who was the potential source of exposure. Based on the source person s history of using anti-hiv drugs, researchers could modify their prescription of PEP. If the treatment history of the potential source was unavailable, researchers gave participants Combivir. In cases where the potential source of infection had a recent viral load above the 50-copy mark, researchers provided Combivir and nelfinavir (Viracept) for PEP.Technicians assessed blood samples before participants began PEP and then three months later, checking for antibodies to HIV, viral load, interferon-gamma and, in some cases, strains of HIV that were resistant to therapy. Results Analysing data from 702 participants, researchers found that there were a total of seven people who became infected with HIV (seroconverters) about 1% of the group. Here s a look at the profile of study participants: The vast majority (95%) was exposed through unprotected sex and were men. The remaining participants were exposed through a combination of sex and needle use or needle use alone. The research team divided participants into two groups seroconverters and non-seroconverters to try to find factors that were linked to HIV infection. All seven seroconverters were men and all had engaged in unprotected, receptive anal intercourse. By comparison, among non-seroconverters, 50% had engaged in similar sex acts. Timing On average, people who seroconverted initiated therapy 46 hours after exposure. Notably, three of seven seroconverters began to take PEP more than 56 hours after exposure. People who did not seroconvert initiated therapy earlier on average 33 hours after exposure. This difference may be important because animal experiments suggest that the sooner PEP is started, the lower the risk of infection. Therapy Of the 14 people (2%) who began PEP with a nelfinavir-containing regimen, none seroconverted. There were no significant differences in the proportion of seroconverters who used Combivir (86%) and non-seroconverters who used Combivir (94%). Adherence Although all seroconverters took PEP for four consecutive weeks, at least three reported that they missed a substantial number of doses, according the research team. Repeated infection(s)? Prior to entering the study, all seroconverters had other, potential exposures to HIV, including unprotected, receptive anal intercourse. To check for the possibility of infection before entering the study, technicians analysed blood samples from participants for HIV viral load. Six of the seven seroconverters were later found to have a viral load less than 50 copies the lower limit of the test, suggesting that there was little chance of prior infection. The remaining participant had a viral load of about 400 copies at the time he entered the study. None of the seroconverters had evidence of HIV that was resistant to any therapy. Why did PEP fail? The researchers note that, as is the case with health care workers, PEP is not 100% effective for preventing infection from sexual exposure to HIV. In this study, there may be several reasons why PEP failed for the seven participants who became HIV seropositive.
1. Better prevention? A possible source of failure is that all people who seroconverted received just two drugs, usually AZT and 3TC. A more robust regimen consisting of a protease inhibitor in addition to two nukes conferred protection to all participants who used it. Other studies have found that a potent protease inhibitor (Kaletra) when used as part of combination therapy for PEP prevented seroconversion in all 88 evaluable people. 2. Continuous exposure Three participants who seroconverted reported that they continued to engage in unprotected, receptive anal intercourse while taking PEP. This may have increased their exposure to HIV, overwhelming their immune systems and PEP. 3. Earlier is better In at least one study with monkeys and simian immunodeficiency virus (SIV), the earlier that PEP was initiated after exposure, the less likely that infection occurred. For instance, PEP was more effective when given at 12 hours postexposure rather than at 72 hours. 4. Adherence More intensive counseling and monitoring of adherence may be a useful intervention to make when conducting future studies of PEP. 5. Route of infection Some researchers said that unprotected, receptive anal intercourse is a severe test for prevention of HIV infection. This arises because of the very high risk of transmission with which this type of sex is associated. However, perhaps more robust PEP regimens may deal with this issue. The San Francisco researchers acknowledge that their study does not allow a true test of the efficacy of PEP because there was no comparison group participants who did not receive PEP. And they emphasize that when exposed patients are being counseled in the future, they should be told that PEP does not provide 100% protection from HIV infection. Continued research on PEP for preventing sexual transmission is needed to find out which combinations of drugs are best for this situation. As well, research with animals to better understand the immunology of the mucosal immune system (in the lining of the anus, mouth, penis and vagina) may provide some insight as to how to strengthen the immune response against HIV in the first hours after infection. Here are some links to guidelines about sexual exposure and PEP from the following countries: United States: http://www.aidsinfo.nih.gov/guidelines/default_db2.asp?id=68 United Kingdom: http://www.bashh.org/guidelines/draft_04/pepse[1]_010404.doc REFERENCES: 1. Roland ME, Neilands TB, Krone MR, et al. Seroconversion following nonoccupational postexposure prophylaxis against HIV. Clinical Infectious Diseases 2005;41(10):1507-13. 2. Cohen MS, Kashuba AD, Gay C. HIV antiretroviral postexposure prophylaxis: a cautionary note. Clinical Infectious Diseases 2005;41(10):1514-6. 3. Merchant RC, Mayer KH. Perspectives on new recommendations for nonoccupational HIV postexposure prophylaxis. JAMA 2005;293(19):2407-9. 4. Rabaud C, Burty C, Grandidier M, et al. Tolerability of postexposure prophylaxis with the combination of zidovudine-lamivudine and lopinavir-ritonavir for HIV infection. Clinical Infectious Diseases 2005;40(2):303-5.
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