Who Should Take Fuzeon? You are most likely to be successful with a regimen containing Fuzeon if: Your CD4 count is more than 100. Your viral load is less than 100,000. You have used 10 or fewer HIV medications. You take Fuzeon with at least two other HIV medications that still work against HIV, as judged by a resistance test.

When Fuzeon was approved in 2003, it was an exciting moment -- it was the first time in seven years that a drug belonging to a new class of HIV medications had been approved. Fuzeon, also known as T-20, or by the generic name enfuvirtide, has been a lifesaver for thousands of HIV-positive people who have run out of treatment options.

Why are there so many people with so few treatment options? One word: resistance. It's something no one likes to hear, but it's more common than you might think. If you have drug-resistant HIV, it simply means that some of your medications no longer work properly.

The most common cause of drug resistance? Not taking your meds regularly. As you probably know, for HIV medications to be successful, each dose must be taken on time at least 95% of the time. You want a steady, constant amount of drug in your body to keep HIV under control. Given the chance, HIV will become resistant to every medicine you take. In fact, many people have become resistant to all HIV medications, including Fuzeon.

Another Class of HIV Meds? Why?

There are currently four "classes," or types, of HIV medications. Each class is fundamentally different and attacks HIV in a way the virus isn't prepared for. The more med classes we have, the more likely it is that you and your doctor will be able to keep one step ahead of HIV and find a way to keep the virus in your body under control. Remember, in general, you need a daily regimen of three or four powerful medications, preferably from two different classes, to dramatically control HIV.

This is where new medications come in. For people who have developed resistance to drugs from each of the currently available classes of medications, having new HIV meds that can work against their resistant virus is extremely important. And if these new meds can battle HIV in a way that's different from older HIV meds, they're even more likely to be successful. That's why a large part of HIV research goes into discovering new classes of HIV meds.

How Does Fuzeon Work?

Enter Fuzeon, the first approved member of a class of drugs called fusion inhibitors. Unlike the other classes of HIV meds -- which attack HIV after it's invaded your immune system -- Fuzeon tries to stop HIV before it gets inside your immune cells. It's one of the newest weapons in our anti-HIV arsenal.

If you can follow our explanation about how HIV enters a CD4 cell -- the box below about co-receptors and glycoproteins and "zipping" -- you'll understand that a good way to attack HIV is by preventing HIV from entering CD4 cells. This is exactly what fusion inhibitors like Fuzeon do. In effect, they prevent HIV from "fusing," or joining, with your CD4 cells, so HIV never has a chance to turn those CD4 cells into new HIV-producing factories (and damage your immune system in the process).

Cold Fusion: How HIV Gets Into Our Cells To damage the immune system, HIV must first get inside your CD4 cells, one of the main cell types responsible for fighting off diseases inside your body. After HIV enters your CD4 cells, it essentially turns them into factories that produce more HIV. Researchers have figured out several of the critical steps that HIV follows to get inside CD4 cells. Here's a play-by-play look: HIV attaches to a CD4 receptor, which is a nub on the outside of the CD4 cell. HIV attaches to a "co-receptor." HIV inserts a harpoon-like anchor called a glycoprotein into the CD4 cell wall. HIV "zips" together the two ends of this anchor (one end is in the CD4 cell; the other is still attached to HIV). This allows HIV to get close enough to the CD4 cell wall so it can fuse with the CD4 cell. (This is the step where Fuzeon works its magic.) An opening is created in the CD4 cell, and -- through a process scientists still do not completely understand -- HIV inserts its genetic code into the CD4 cell. This allows HIV to begin the process of turning the CD4 cell into an HIV factory.

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