Fuzeon (Enfuvirtide) – Subcutaneous

What Is Fuzeon?

Fuzeon (enfuvirtide) is an injectable prescription medication used to treat the human immunodeficiency virus (HIV) infection in treatment-experienced people who are at least 6 years old and weigh at least 24 pounds.

Fuzeon is used in combination with other antiretroviral agents for individuals experiencing HIV-1 replication (the process in which HIV continuously spreads in the body) despite ongoing antiretroviral therapy.

This medication is classified as an HIV entry and fusion inhibitor. Moreover, as an antiretroviral agent, Fuzeon works by stopping the virus from duplicating inside the body. As a result, this allows the immune system to fix itself and stop further damage.

Fuzeon is often used alongside other drugs because HIV can quickly adapt and become resistant. Specifically, Fuzeon works by blocking HIV from fusing with and infecting healthy CD4 T cells—the immune cells HIV targets to weaken your immune system.

Fuzeon is an injectable medication given subcutaneously, meaning under the skin. You inject the drug into the layer of tissue found between the skin and muscle using a small needle.

As a result, enfuvirtide, the active ingredient in Fuzeon, is absorbed more slowly than if injected into a vein.

This article will focus on the subcutaneously injected Fuzeon.

Drug Facts

Generic Name: Enfuvirtide
Brand Name: Fuzeon
Drug Availability: Prescription
Administration Route: Injection
Therapeutic Classification: Antiretroviral agent
Available Generically: No
Controlled Substance: N/A
Active Ingredient: Enfuvirtide
Dosage Form(s): Subcutaneous injection

What Is Fuzeon Used For?

Fuzeon is approved by the Food and Drug Administration (FDA) to treat HIV infection in people whose previous drug regimens have failed—meaning you continue to have detectable levels of HIV in your blood (viral load), despite taking HIV medicines. Fuzeon is always used in combination with other HIV medications.

For context, HIV is a disease that attacks the immune system and weakens a person's defense against infections and subsequent ability to fight off invading cancerous cells.

As the virus destroys the ability of immune cells to properly function, infected people can become immunodeficient (meaning their immune system is compromised). Of note, immune function is typically measured by healthcare professionals by gauging a person's CD4 cell count.

Fuzeon can’t cure HIV, but it can decrease your chance of developing AIDS (acquired immunodeficiency syndrome) or HIV-related conditions, such as serious infections and cancer.

Fuzeon can also help prevent you from spreading HIV to others when used in combination with other HIV medications, safe sex practices, and lifestyle changes.

How to Take Fuzeon

Fuzeon is a medication that you inject under the skin. It is typically taken twice per day. Fuzeon comes as a powder that you'll need to mix with sterile water. Your healthcare provider will show you how to prepare and administer your dose or instruct the person who will administer your dose.

Each Fuzeon kit comes with vials of Fuzeon powder (one dose per vial), vials of sterile water, and syringes and needles for mixing and injecting your dose. You will also need alcohol pads to clean the vials and your skin and a sharps container to dispose of used needles and syringes.

If you do not have an FDA-cleared sharps disposal container, you may use a household container that is puncture resistant, leak resistant, made of heavy-duty plastic, and sealable. An empty laundry detergent container is one option.

Wash your hands well before preparing your dose. Follow the instructions provided with your prescription for mixing Fuzeon powder with sterile water. Always mix Fuzeon with sterile water—never use tap water.

Following the instructions, inject your dose of Fuzeon into your upper arm, stomach, or the front of your thighs. Rotate your injection sites, and never administer a dose of Fuzeon into the same spot two times in a row. Avoid any sites that have an injection reaction from a previous dose.

Do not administer Fuzeon:

  • Into or around your navel (belly button)
  • In an area under a belt or waistband
  • Near the elbows, knees, groin, or lower or inner buttock
  • Into skin that has a tattoo, burn, mole, bruise, or scar 

After you inject your dose, place the needle and syringe into your sharps disposal container. Never reuse needles or syringes—this can lead to a serious infection.

When the container is almost full, follow the instructions on this FDA website to properly dispose of your sharps container based on where you live.


Fuzeon should be stored at room temperature. You may find it convenient to prepare both your morning and evening doses at the same time. If you do this, keep the mixed vial in the refrigerator and use it within 24 hours.

Do not store your dose in a syringe. Be sure to keep Fuzeon and all of your medications in a safe location, out of the reach of children. Avoid storing in a bathroom.

How Long Does Fuzeon Take to Work?

Healthcare providers typically measure the amount of HIV in your blood (viral load) before starting a new HIV drug regimen, and then routinely after beginning treatment.

A decrease in the amount of HIV in your blood lets healthcare providers know your HIV medications are working. If your HIV drug regimen is effective, you should have very low levels of HIV in your blood (viral suppression) within eight to 24 weeks after starting treatment. Healthcare providers also measure your CD4 T-cell count to see how well your immune system is working.

What Are the Side Effects of Fuzeon?

This is not a complete list of side effects, and others may occur. A healthcare provider can advise you on side effects. If you experience other effects, contact your healthcare provider. You may report side effects to the FDA at fda.gov/medwatch or 800-FDA-1088.

Common Side Effects

Almost all people that use Fuzeon experience some reactions at the injection site. As such, potential reactions may include:

  • Bruising 
  • Hardening of the skin or a bump where you’ve injected your dose 
  • Itching
  • Pain or discomfort 
  • Redness

Let your healthcare provider know if these reactions don’t go away within a few days or if they get worse. 

Other common side effects include:

Severe Side Effects

Fuzeon may sometimes cause severe reactions. Let your healthcare provider know right away if you experience any serious side effects. Call 911 if your symptoms feel life-threatening or you think you’re having a medical emergency.

Serious side effects and their symptoms include the following:

Severe injection site reactions or infections: Let your healthcare provider know if you have redness, pain, swelling, or oozing at the injection site that does not go away after a few days or that gets worse.

Neuralgia (nerve pain) or numbness, burning, or paresthesia (prickling feeling of the skin): These side effects have happened to people who use the Biojector 2000 (a special needle-free device) to inject their dose of Fuzeon. Symptoms can last for up to six months.

Bleeding at the injection site: You may be at increased risk of bleeding if you take blood thinners or have hemophilia or other blood-clotting problems. 

Allergic reaction: Seek emergency medical care right away if you develop any of the following:

Pneumonia: People taking Fuzeon have developed pneumonia, which in some cases led to death. Seek medical care if you develop a cough with a fever, fast breathing, or shortness of breath.

Changes in your immune system (immune reconstitution syndrome): After starting a new HIV medicine, your immune system sometimes begins to fight infections you didn’t know you had. This can happen even after you’ve taken Fuzeon for several months. Let your healthcare provider know if you develop any new symptoms, including fever, sore throat, weakness, cough, or shortness of breath.

Pancreas problems (pancreatitis): Let your healthcare provider know right away if you develop very bad stomach or back pain, nausea, or vomiting.

Report Side Effects

Fuzeon may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your healthcare provider may send a report to the FDA's MedWatch Adverse Event Reporting Program online or by phone (800-332-1088).

Dosage: How Much Fuzeon Should I Take?

Drug Content Provided and Reviewed by IBM Micromedex®

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For injection dosage form (solution):
    • For treatment of HIV infection:
      • Adults—90 milligrams (mg) (1 milliliter [mL]) injected under the skin 2 times a day.
      • Children 6 years of age and older—Dose is based on weight and must be determined by your doctor.
        • Weighing 42.6 kilograms (kg) or more—90 milligrams (mg) (1 milliliter [mL]) injected under than skin 2 times a day.
        • Weighing 38.1 to 42.5 kg—81 mg (0.9 mL) injected under than skin 2 times a day.
        • Weighing 33.6 to 38.0 kg—72 mg (0.8 mL) injected under than skin 2 times a day.
        • Weighing 29.1 to 33.5 kg—63 mg (0.7 mL) injected under than skin 2 times a day.
        • Weighing 24.6 to 29.0 kg—54 mg (0.6 mL) injected under than skin 2 times a day.
        • Weighing 20.1 to 24.5 kg—45 mg (0.5 mL) injected under than skin 2 times a day.
        • Weighing 15.6 to 20.0 kg—36 mg (0.4 mL) injected under than skin 2 times a day.
        • Weighing 11.0 to 15.5 kg—27 mg (0.3 mL) injected under than skin 2 times a day.
      • Children younger than 6 years of age and weighing less than 11 kilograms (kg)—Use and dose must be determined by your doctor.


Potential consumers of Fuzeon should note the following before starting treatment:

Pregnancy: The safety data of this medicine in pregnancy is limited, therefore its routine use during pregnancy should be discussed with your healthcare provider.

Of note, there is a pregnancy registry for people who use antiretroviral medicines during pregnancy. The purpose of this registry is to collect information about the health of the parent and the baby. Talk to your healthcare provider about how you can take part in this registry.

Nursing: The Centers for Disease Control and Prevention (CDC) recommends that HIV-1-infected parents not breastfeed their infants to avoid the risk of postnatal transmission of HIV-1. 

Children: The use of Fuzeon in children weighing at least 24 pounds is supported by evidence from studies of Fuzeon in adults and by two pediatric studies evaluating the safety and efficacy of Fuzeon in people 6 and older.

Despite being FDA-approved for children 6 years and older, the latest HIV treatment guidelines do not recommend using Fuzeon in children.

Adults 65 and older: Studies on the efficacy and safety of Fuzeon did not include enough people 65 and over to safely determine whether they respond differently from younger people.

Therefore, caution should be used in the administration and monitoring of Fuzeon in people 65 and older to reflect the potential for more frequent liver, kidney, or heart dysfunction.

Missed Dose

If you forget to take your dose, take it as soon as you remember. If it’s almost time for your next dose, skip the missed dose and take your next dose at the regular time. Do not double up doses or take extra.

Missing doses or stopping Fuzeon without talking to your healthcare provider can make your HIV-1 infection harder to treat. When your supply of Fuzeon begins to run low, call your healthcare provider for a refill to ensure you don’t miss any doses. 

Overdose: What Happens If I Take Too Much Fuzeon?

There are no cases of human overdose with Fuzeon. Therefore, healthcare providers aren't certain what effects a Fuzeon overdose would cause.

Nonetheless, if you fear you may have taken too much Fuzeon, call your healthcare provider right away. They’ll likely monitor your condition closely to ensure you remain healthy. If you develop symptoms that feel life-threatening, call 911.

What Happens If I Overdose on Fuzeon?

If you think you or someone else may have overdosed on Fuzeon, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Fuzeon, call 911 immediately.


Drug Content Provided and Reviewed by IBM Micromedex®

It is very important that your doctor check you your child's progress at regular visits, especially during the first few weeks that you use this medicine. Blood and urine tests may be needed to check for any unwanted effects.

This medicine may cause serious allergic reactions, which can be life-threatening and require immediate medical attention. Tell your doctor right away if you have a rash, itching, hoarseness, trouble breathing or swallowing, or any swelling of your hands, face, or mouth after using this medicine.

This medicine may increase the risk of having pneumonia. This is more likely to occur if you smoke or have a history of lung disease. Check with your doctor right away if you have chest pain or tightness, cough, fever, chills, or troubled breathing.

This medicine can cause reactions at the injection site. Almost all people get injection site reactions with enfuvirtide. These reactions hurt and itch, and they are usually mild to moderate but can occasionally be severe. These reactions generally happen within the first week of treatment and as you keep using enfuvirtide. If the injection site nodules drain pus or cause redness that spreads or streaks from the sites, or you are worried about the reaction you are having, call your doctor right away.

Some people who have used Biojector® 2000 to inject this medicine have had shooting nerve pain and tingling lasting up to 6 months when injected close to large nerves or near joints, or had bleeding, bruising, or lumps. Talk to your doctor if you have concerns about this.

Your immune system may get stronger when you start using HIV medicines. Tell your doctor right away if you notice any changes in your health. Sometimes the immune system will start to fight infections that were hidden in your body, such as pneumonia, herpes, or tuberculosis. Autoimmune disorders (eg, Graves' disease, polymyositis, and Guillain-Barré syndrome) may also occur.

This medicine may make you dizzy or drowsy. Do not drive or do anything else that could be dangerous until you know how this medicine affects you.

This medicine does not decrease the risk of transmitting the HIV infection to others through sexual contact or by contaminated blood. Make sure you understand and practice safe sex, even if your partner also has HIV. Avoid sharing needles with anyone.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

What Are Reasons I Shouldn’t Take Fuzeon?

Don’t take Fuzeon if you are allergic to enfuvirtide or any ingredient in Fuzeon, including mannitol.

When studying the effectiveness of Fuzeon, an increased rate of bacterial respiratory infection (i.e., pneumonia) was observed in people treated with enfuvirtide in phase III clinical trials. Therefore, your healthcare provider may monitor you for signs of pneumonia, especially if you have any prior conditions which may predispose you to pneumonia.

What Other Medications Interact With Fuzeon?

Using Fuzeon with blood thinners, or medications that affect how well your blood clots, can increase your risk of bleeding.

Therefore, alert your healthcare provider if you take any of the following:

This is not a complete list of all the drugs that may interact with Fuzeon. Always keep an updated list of all the medicines you take and let your doctor and pharmacist know anytime there are changes.

What Medications Are Similar?

Antiretroviral agents similar to Fuzeon used to treat the symptoms of HIV infection include:

  • Reyataz (atazanavir)
  • Prezista (darunavir)
  • Lexiva (fosamprenavir)
  • Viracept (nelfinavir)
  • Norvir (ritonavir)

This is a list of drugs also used similarly to Fuzeon. It is not necessarily a list of medications recommended to take together. You should not take these drugs together unless your healthcare provider tells you to. Talk to your pharmacist or healthcare provider if you have questions.

Frequently Asked Questions

  • What is Fuzeon used for?

    Fuzeon is used with other medications to treat HIV infection in people that have failed previous treatments.

  • How does Fuzeon work?

    Fuzeon is a fusion inhibitor. It prevents HIV from infecting healthy CD4 T-cells, which play an important role in your immune system.

  • How will you know if Fuzeon is working?

    Your healthcare provider will measure the amount of HIV in your blood before and after starting Fuzeon.

    If Fuzeon is effective, blood levels of HIV should be very low by eight to 24 weeks of treatment. Your healthcare provider will also measure your CD4 T-cell levels to see how well your immune system is working.

  • What are the most common side effects of Fuzeon?

    The most common side effects of Fuzeon are injection site reactions, including bruising, hardening of the skin, a bump at the injection site, itching, pain, and redness. Let your healthcare provider know if these reactions don’t go away after a few days, or if they continue to get worse.

  • Where is Fuzeon injected?

    Only inject Fuzeon into the stomach (not in or near the belly button), upper arm, or front of the thighs. Do not inject into the skin with a tattoo, burn, mole, bruise, or scar. Do not inject Fuzeon into the same spot two times in a row or where there is a reaction from a previous dose.

How Can I Stay Healthy While Taking Fuzeon?

Finding out your HIV medications aren’t working can be frustrating and scary—especially if you’ve tried several different regimens. Fortunately, Fuzeon is one option that may be able to help.

Because Fuzeon is an injectable medicine, you (or the person injecting your dose) must learn how to administer it.

Let your healthcare provider know if you have any questions since injecting the wrong way can lead to side effects. Fuzeon, like many HIV drugs, may cause serious side effects.

Be sure to review the warnings associated with Fuzeon each time you pick up your prescription.

Let your healthcare provider know right away if you notice any unusual symptoms. Quickly identifying an adverse reaction can help keep you safe.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and is not intended to replace medical advice, diagnosis, or treatment from a healthcare provider. Consult your healthcare provider before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Food and Drug Administration. Fuzeon (enfuvirtide) prescribing information.

  2. MedlinePlus. Enfuvirtide Injection.

  3. HIV.gov. HIV treatment overview.

  4. National Cancer Institute. Combination antiretroviral therapy.

  5. ScienceDirect. Enfuvirtide.

  6. Kim H, Park H, Lee SJ. Effective method for drug injection into subcutaneous tissueSci Rep. 2017;7(1):9613. Published 2017 Aug 29. doi:10.1038/s41598-017-10110-w

  7. Centers for Disease Control and Prevention. About HIV/AIDS.

  8. HIVinfo.NIH.gov. Guidelines for the use of antiretroviral agents in adults and adolescents with HIV. Plasma HIV-1 RNA (viral load) and CD4 count monitoring.

  9. HIVinfo.NIH.gov. Drug database: enfuvirtide.

  10. Prescribers' Digital Reference. Enfuvirtide - drug summary.

  11. Lv Z, Chu Y, Wang Y. HIV protease inhibitors: a review of molecular selectivity and toxicityHIV AIDS (Auckl). 2015;7:95-104. doi:10.2147/HIV.S79956

By Christina Varvatsis, PharmD
Christina Varvatsis is a hospital pharmacist and freelance medical writer. She is passionate about helping individuals make informed healthcare choices by understanding the benefits and risks of their treatment options.