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Pill may cut HIV risk as much as 99%

Sept. 12, 2012
Courtesy of the Gladstone Institutes
and World Science staff

Daily use of a pill ap­proved to pro­tect against HIV in­fec­tion cuts a man’s risk of get­ting the vi­rus by 99 per­cent, a new study in­di­cates.

The re­search al­so of­fers the first ev­i­dence that even im­pe­r­fect ad­her­ence to the treat­ment reg­i­men can pro­vide a big re­duc­tion in the risk of ac­quir­ing the vi­rus, which causes AIDS. Par­ti­ci­pants in the re­search were found to be able to cut their HIV in­fec­tion risk by 76 pe­r­cent merely by tak­ing two doses a week.

The stu­dy, pub­lished in the Sept. 12 on­line is­sue of the re­search jour­nal Sci­ence Transla­t­ional Med­i­cine, ex­am­ines the ef­fec­tive­ness of a FDA-ap­proved drug known as teno­fovir diso­proxil fu­marate (brand name Tru­vada).

The re­search builds on a 2010 study by Rob­ert Grant at the Uni­vers­ity of Cal­i­for­nia, San Fran­cis­co and the Glad­stone In­sti­tute in San Fran­cis­co, along with col­leagues. The team found that Tru­vada—which had been used for years to treat HIV-positive pa­tients—could al­so pre­vent new in­fec­tions in peo­ple likely to come in con­tact with the vi­rus. 

But ques­tions about the drug’s real-world ef­fec­tive­ness re­mained—in par­ticu­lar con­cern­ing the is­sue of ad­her­ence to a reg­i­men of a pill a day. “There was con­cern that the pro­tective ef­fect of Tru­vada was frag­ile, and that in­di­vid­u­als tak­ing the drug would need to ad­here pe­r­fectly to daily reg­i­men for it to work,” said Grant. “This new study sug­gests that Tru­vada can help block the vi­rus even if the pe­r­son on a daily reg­i­men does­n’t al­ways ad­here pe­r­fectly.”

The study ex­am­ined the risk of HIV ac­qui­si­tion in men who have sex with men. Par­ti­ci­pants dif­fer­ent doses of the drug. Men came in­to a clin­ic eve­ry day and were giv­en ei­ther two pills per week, four pills per week or se­ven pills per week. The re­search­ers then com­pared drug con­centra­t­ions from their study to drug con­centra­t­ions from a pre­vi­ous stu­dy. 

The re­search team es­ti­mates that par­ti­ci­pants could re­duce their risk of HIV by 76 pe­r­cent tak­ing two doses per week, 96 pe­r­cent by tak­ing four doses per week, and 99 pe­r­cent by tak­ing se­ven doses per week. 

The tim­ing of the dos­ing rel­a­tive to sex­u­al in­ter­course likely mat­ters, based on re­search done in non-human pri­ma­tes, al­though this could not be in­ves­t­i­gated in de­tail in peo­ple, the re­search­ers added. High­er drug con­centra­t­ions and more fre­quent use may be re­quired for wom­en be­cause the drugs are not con­centrated as much in the fe­male gen­i­tal tract, the au­thors not­ed. 

“Pa­tients should still take one pill a day to achieve the best re­sults, and we en­cour­age peo­ple to ex­plore mul­ti­ple meth­ods to pre­vent HIV—such as reg­u­lar con­dom use, early treat­ment of HIV in­fec­tion in part­ners, good com­mu­nica­t­ion and male cir­cum­ci­sion,” Grant said. “We hope that our find­ings lead to more ef­fective use of pre­vention tools that fi­nally squash the HIV/AIDS epi­dem­ic.”


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Daily use of a pill approved to protect against HIV infection cuts a man’s risk of getting the virus by 99%, a new study indicates. The research also offers the first evidence that even imperfect adherence to the treatment regimen can provide a big reduction in the risk of acquiring the virus, which causes AIDS. Participants in the research were found to be able to cut their HIV infection risk by 76 percent merely by taking two doses a week. The study, published in the Sept. 12 online issue of the research journal Science Translational Medicine, examines the effectiveness of a FDA-approved drug known as tenofovir disoproxil fumarate (brand name Truvada). The research builds on a 2010 study by Robert Grant at the University of California, San Francisco and the Gladstone Institute in San Francisco, along with colleagues. The team found that Truvada—which had been used for years to treat HIV-positive patients—could also prevent new infections in people likely to come in contact with the virus. But questions about the drug’s real-world effectiveness at preventing HIV transmission remained—particularly concerning the issue of adherence to a regimen of taking a pill every day. “There was concern that the protective effect of Truvada was fragile, and that individuals taking the drug would need to adhere perfectly to daily regimen for it to work,” said Grant. “This new study suggests that Truvada can help block the virus even if the person on a daily regimen doesn’t always adhere perfectly.” The study examined the risk of HIV acquisition in men who have sex with men. Participants different doses of the drug. Men came into a clinic every day and were given either two pills per week, four pills per week or seven pills per week. The researchers then compared drug concentrations from their study to drug concentrations from a previous study. The research team estimates that participants could reduce their risk of HIV by 76 percent taking two doses per week, 96 percent by taking four doses per week, and 99 percent by taking seven doses per week. The timing of the dosing relative to sexual intercourse likely matters, based on research done in non-human primates, although this could not be investigated in detail in people, the researchers added. Higher drug concentrations and more frequent use may be required for women because the drugs are not concentrated as much in the female genital tract, the authors noted. “Patients should still take one pill a day to achieve the best results, and we encourage people to explore multiple methods to prevent HIV—such as regular condom use, early treatment of HIV infection in partners, good communication and male circumcision,” Grant said. “We hope that our findings lead to more effective use of prevention tools that finally squash the HIV/AIDS epidemic.”