From Mark Cichocki, R.N.,
Your Guide to AIDS / HIV.
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About.com Health's Disease and Condition content is reviewed by Susan Olender, MD

Since the advent of Protease Inhibitors and other HIV medications, people infected with HIV have lived longer, healthier lives. But in recent years we have see an increasing concern over resistance to current HIV meds, toxic side effects, and adherence problems related to side effects and pill burden. In an effort to halt this trend, the newest class of drug has hit the market. Uniquely different from other HIV meds, entry inhibitors fight the virus in an entirely different way. Let's take a closer look at entry inhibitors.

What are fusion inhibitors?
To understand what fusion inhibitors are and how they work, we first must understand how HIV attacks our healthy T-cells. The HIV virus, like any virus, lacks the ability to support life on its own. In order to survive and reproduce, the virus must attach to a living "host" cell which provides the virus with the environment it needs to live and multiply.

The HIV virus finds the assistance it needs by way of the immune system's T-cells. Once HIV enters the human body, it locates these T-cells and attaches to them, injecting genetic material into the T-cell, beginning the reproductive process. But how does the virus attach to T-cells? Think of it as a key and a lock. Specific binding sites on the outer envelope of the HIV virus attach to corresponding sites on the T-cell. Just as a key slips into a lock, the virus attaches and opens the cell in order to inject its genetic material.

Fusion inhibitors work by binding to the attachment sites of the HIV virus. With their attachment sites already filled, HIV can't attach to the T-cell and therefore can't reproduce. Because the keyhole is already filled, the HIV "key" can't be inserted into the T-cell "lock" and therefore the cell "door" can't be opened. Because it can't enter the T-cell, the virus has no "host" to aid in its reproduction and is unable to infect the body.

How do fusion inhibitors differ from existing HIV medications?
Fusion inhibitors are generating excitement in the HIV community mainly because they attack HIV in an entirely different way than existing HIV medications. While current medications fight HIV after it has entered the T-cell, fusion inhibitors attack HIV before it has a chance to gain access to the T-cell, preserving the cell's integrity and therefore preserving the immune system's health. While there is only one entry inhibitor available at this time, Fuzeon, more are on the horizon, bring hope that a new type of drug will give the boost we need to affectively fight this disease.