ENFUVIRTIDE (Fuzeon)

WHAT IS ENFUVIRTIDE?
Enfuvirtide, also called FuzeonŽ or T-20, is a drug used as part of antiretroviral therapy (ART). It is manufactured by Roche and Trimeris.

Enfuvirtide is the first "fusion inhibitor" drug. When HIV infects a cell, it attaches to the outside of the cell. Then it "fuses" or joins itself with the cell. Enfuvirtide stops this process of fusion. This means that HIV cannot infect that cell.
WHO SHOULD TAKE IT?
Enfuvirtide was approved in 2003 as an antiretroviral drug (ARV) against HIV. It was studied in adults and in children over 6 months of age. It is recommended only when other ART has not worked.

There are no absolute rules about when to start ART. You and your health care provider should consider your CD4 cell count, your viral load, any symptoms you are having, and your attitude about taking ART. Fact Sheet 404 has more information about guidelines for the use of ART.

Enfuvirtide is injected twice a day. It will most likely be used by people who have very few choices of ARVs in pill form.

If you take enfuvirtide with other ARVs, you can reduce your viral load and increase your CD4 cell counts. This should mean staying healthier longer.
WHAT ABOUT DRUG RESISTANCE?
The HIV virus is sloppy when it makes copies of its genetic code (RNA). Many new copies of HIV are mutations: they are slightly different from the original virus. Some mutations can continue to multiply even when you are taking an ARV. When this happens, the drug will stop working. This is called "developing resistance" to the drug. See Fact Sheet 126 for more information on resistance.

Resistance to enfuvirtide can develop quickly if it is taken by itself. With combination therapy (taking more than one ARV at the same time), HIV mutates much more slowly. Resistance takes longer to develop. It is very important to take ARVs according to instructions, on schedule, and not to skip or reduce doses. Recent research showed that enfuvirtide can be effective even when HIV appears to have some resistance to it.

Sometimes, if you develop resistance to one drug, you will also have resistance to other ARVs. This is called "cross-resistance." Enfuvirtide does not have cross-resistance with any other ARVs.
HOW IS ENFUVIRTIDE TAKEN?
If enfuvirtide is swallowed, it is destroyed by stomach acids. This means that it cannot be taken in pill form. Enfuvirtide is injected just under the skin. This is called a "subcutaneous" injection.

The adult dosage of enfuvirtide is 90 mg per injection, twice a day. The dosage for children is based on their body weight. Once-daily injections of enfuvirtide are being studied.

If your health care provider prescribes enfuvirtide, you will shown how to prepare each injection, and how and where to inject it. It can take about 40 minutes to prepare a dose of enfuvirtide. You can prepare both of a day?s doses at the same time. Avoid injecting near large nerves (ask your health care provider). Also, don?t inject where you have had a reaction from a previous injection or into moles, tattoos, scar tissue, bruises, or your navel.

A new injector (the Biojector) does not use needles. It causes fewer reactions at the injection sites. However, it can cause nerve pain lasting up to 6 months. Patients with hemophilia or who bruise easily may have problems with the Biojector.

Enfuvirtide is a new class of ARV. This means that it is active against HIV that has developed resistance to any other ARV. However, it cannot be used by itself. It must be combined with other ARVs.
WHAT ARE THE SIDE EFFECTS?
The most common side effects of enfuvirtide are skin reactions where the drug is injected. Almost everybody who uses enfuvirtide gets these reactions. They can be very mild, such as slight redness. They can include itching, swelling, pain, hardened skin, or hard lumps. Each reaction might last up to a week.

With two injections each day, people using enfuvirtide might have reactions at several spots on their body at the same time. Very few patients have stopped using it because of skin reactions.

The most common other side effects of enfuvirtide are headache, pain and numbness in feet or legs, dizziness, and loss of sleep.
HOW DOES IT REACT WITH OTHER DRUGS?
Enfuvirtide has been studied to see if it interacts with other drugs. Enfuvirtide may increase blood levels of tipranavir and ritonavir. There are very few known interactions with other ARVs. Enfuvirtide has not been studied with all medicines, over-the-counter drugs, or vitamin or herbal supplements. Be sure your health care provider knows about all medications and supplements that you are taking.
THE BOTTOM LINE
Enfuvirtide is the first drug in a new class. It stops HIV from "fusing" with a cell it has attached to. This prevents HIV from infecting the cell. Enfuvirtide helps control HIV, even when it is resistant to other medications.

Enfuvirtide has to be injected under the skin twice daily. Almost everyone who uses it gets skin reactions where it is injected. Most of these are not serious.