How Truvada Works and Why It Can Prevent HIV
Using Truvada for HIV Prevention
Truvada is also approved for preventing HIV in certain high-risk populations. This is known as pre-exposure prophylaxis. For this use, Truvada should be combined with safer sex practices in people who are confirmed to be HIV negative with tests before treatment and at least every three months during treatment.
It is important to get tested for HIV frequently while using Truvada for prevention. This is because the drug is not 100 percent effective, and because using the drug for prevention in someone who already has HIV increases the risk of developing drug-resistant HIV, which does not respond well to medications.
It is important to understand that the drug simply reduces the chances of getting HIV -- it does not eliminate the risk. In studies, Truvada reduces the risk of getting HIV by 42 percent (in men who have sex with men) or 75 percent (in heterosexual couples with one HIV-positive partner and one HIV-negative partner).
How Does Truvada Work?
Tenofovir (one of the components of Truvada) is currently the only medication in a class of HIV medications known as nucleotide reverse transcriptase inhibitors (NtRTIs). Emtricitabine (the other component) belongs to a group of medications known as nucleoside reverse transcriptase inhibitors (NRTIs). Both medications work similarly to block a process that the HIV virus needs in order to multiply.
Like other viruses, HIV must use a person's own cells to reproduce. However, HIV is a little different from many other viruses because it must first convert its genetic material from RNA to DNA. It is the DNA genes that allow HIV to multiply.
HIV converts its genetic material by using a special protein called the reverse transcriptase enzyme. To create DNA, this enzyme uses several different molecular building-blocks.
Truvada works by tricking reverse transcriptase into thinking it is one of these molecular building-blocks. However, it is just different enough that when used to create DNA, Truvada actually stops the DNA from being made. Without DNA, HIV cannot multiply. Truvada is not a cure for HIV or AIDS, however. It can help stop HIV from infecting healthy cells in the body, but it does not help cells that have already been infected with the virus.