HIV drugs have long been used to prevent new infections in HIV-negative individuals.
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Post-exposure prophylaxis (PEP) is one strategy that involves the use of HIV drugs to prevent infection AFTER the person is exposed to the virus. In this case, the HIV medicines must be administered very soon after the exposure. Post-exposure prophylaxis was first developed to protect hospital and clinic workers from becoming infected after accidental needle-sticks with HIV-infected blood or from blood of a person whose HIV status was unknown.
In cases of rape, HIV meds may be used to protect the victim when the HIV status of the rapist is not known. Again, these meds must be taken very soon after the incident. In resource-poor countries that can’t afford to provide full HIV-treatment for pregnant women, HIV medicines are provided to the mother at the time of delivery to reduce the risk of infecting the new infant. This practice has dramatically reduced mother-to-child transmission of HIV.
Most recently, some very strategic studies have shown us that when an HIV-infected individual is faithfully taking their medicine, and their HIV in under control (undetectable levels of virus in the blood), their HIV-negative partner almost never gets infected – even without using male or female condoms.
Now, we’re talking about using drugs in HIV-negative people BEFORE they are exposed to HIV through unprotected sex with an infected person. This is called pre-exposure prophylaxis (PrEP). By this method, a person who is HIV-negative is taking medicines on a daily basis so that if they have sex with an infected person, the medicines are already in their tissues and can block HIV from infecting them.
Pre-exposure prophylaxis has been tested in many countries. In the US, the FDA-approved two potent HIV medicines combined in a single pill based on its ability to protect people at high risk for infection from being infected. The medicines Tenofovir (te-NO-FO-vir) and Emtricitibine (em-try-SY-toe-bean) are combined into a single pill product called Truvada (True-VA-da).
For HIV treatment, tenofovir and emtricibine must be combined with a third potent drug from a different class for maximal HIV suppression, yet taking this two-drug combo is effective for prevention. One study used pre-exposure prophylaxis in a group of HIV-negative MSM’s (men-who have sex-with men) who were having high rates of unprotected sex.
In this study those who were randomized to take the medicines had significantly lower rates of HIV infections than those not randomized to get the medicines. Another study looked at the use of PrEP in heterosexual couples where one partner was positive and the other partner negative. The negative partner gained significant protection from infection by taking pre-exposure prophylaxis.
As I stated above, the use of HIV medicines for treatment in the infected partner in a discordant couple (one partner is HIV+ and the other is HIV-) can protect the uninfected partner. However, the infected partner may not always take their medicines properly. Besides, there are other problems that can reduce the effect of the meds on transmitting the virus (such as having another STD). So by using PrEP, the negative partner has control over the situation by being able to protect themselves.
One of the biggest challenges in HIV management is getting patients to consistently take their medicine as prescribed. This remains the major reason why treatment regimens “fail” and HIV disease progresses.