Medical Editor: John P. Cunha, DO, FACOEP Last updated on RxList: 11/11/2021
Fuzeon Side Effects Center

What Is Fuzeon?

Fuzeon (enfuvirtide) is a type of antiviral medication called a fusion inhibitor used to treat HIV, which causes acquired immunodeficiency syndrome (AIDS), and is usually given after other medications have been tried without successful treatment of HIV. Fuzeon is not a cure for HIV or AIDS.

What Are Side Effects of Fuzeon?

Common side effects of Fuzeon include:

  • pain,
  • irritation,
  • redness,
  • itching,
  • bruising,
  • swelling,
  • hardened skin, or
  • bumps at the injection site.

These types of reactions are common and may last up to 7 days. Other side effects of Fuzeon include:

  • runny or stuffy nose,
  • constipation,
  • pain or numbness in your feet or legs,
  • tired feeling,
  • muscle weakness or loss of strength,
  • muscle pain,
  • sleep problems (insomnia), or
  • depression.

Tell your doctor if you have serious side effects of Fuzeon including:

  • unexplained weight loss,
  • persistent muscle aches or weakness,
  • joint pain,
  • numbness or tingling of the hands/feet/arms/legs,
  • severe tiredness,
  • vision changes,
  • severe or persistent headaches,
  • signs of infection (such as fever, chills, trouble breathing, cough, non-healing skin sores),
  • signs of an overactive thyroid (such as irritability, nervousness, heat intolerance, fast/pounding/irregular heartbeat, bulging eyes, unusual growth in the neck/thyroid known as a goiter),
  • signs of a certain nerve problem known as Guillain-Barre Syndrome (such as difficulty breathing/swallowing/moving your eyes, drooping face, paralysis, slurred speech),
  • anxiety,
  • numbness/tingling/shooting nerve pain near injection site,
  • signs of injection site infection (such as oozing, warmth, persistent pain and redness),
  • abdominal pain, or
  • loss of appetite.

Dosage for Fuzeon

The recommended dose of Fuzeon is 90 mg (1 mL) twice daily injected subcutaneously into the upper arm, anterior thigh or abdomen.

What Drugs, Substances, or Supplements Interact with Fuzeon?

Fuzeon may interact with blood thinners. Tell your doctor all medications and supplements you use.

Fuzeon During Pregnancy or Breastfeeding

Fuzeon should be used only when prescribed during pregnancy. It is unknown if this drug passes into breast milk. Because breast milk can transmit HIV, do not breastfeed.

Additional Information

Our Fuzeon (enfuvirtide) Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


What is HIV? See Answer
Fuzeon Consumer Information

Get emergency medical help if you have signs of an allergic reaction: skin rash or hives; fever with vomiting; blood in your urine; difficulty breathing; fainting; swelling of your feet, face, lips, tongue, or throat.

Call your doctor at once if you have:

  • shortness of breath;
  • fever, chills, chest congestion, cough with yellow or green mucus, stabbing chest pain, wheezing;
  • fever with vomiting and skin rash;
  • severe pain in your upper stomach spreading to your back, nausea and vomiting;
  • blood in your urine;
  • swelling in your feet;
  • a skin reaction (itching, redness, swelling, pain, or a hard lump) where the medicine is injected; or
  • pain, warmth, oozing, or redness where an injection was given, especially if these symptoms get worse or last longer than 7 days.

Enfuvirtide affects your immune system, which may cause certain side effects (even weeks or months after you've taken this medicine). Tell your doctor if you have:

  • signs of a new infection--fever, night sweats, swollen glands, cold sores, cough, wheezing, diarrhea, weight loss;
  • trouble speaking or swallowing, problems with balance or eye movement, weakness or prickly feeling; or
  • swelling in your neck or throat (enlarged thyroid), menstrual changes, impotence.

Common side effects may include:

  • nausea, loss of appetite, constipation, diarrhea;
  • numbness or pain in your legs or feet;
  • muscle pain or weakness;
  • depressed mood;
  • swollen glands, runny or stuffy nose;
  • weight loss;
  • tiredness, trouble sleeping, tired; or
  • pain, swelling, burning, or irritation where the medicine was injected.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Read the entire detailed patient monograph for Fuzeon (Enfuvirtide)


A Timeline of the HIV/AIDS Pandemic See Slideshow
Fuzeon Professional Information


The following adverse reactions are discussed in greater detail in other sections:

  • Administration with Biojector® 2000 [see WARNINGS AND PRECAUTIONS]
  • Hypersensitivity Reactions [see WARNINGS AND PRECAUTIONS]

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

The overall safety profile of FUZEON is based on 2131 subjects who received at least 1 dose of FUZEON during various clinical trials. This includes 2051 adults, 658 of whom received the recommended dose for greater than 48 weeks, and 63 pediatric subjects.

Assessment of treatment-emergent adverse events is based on the pooled data from the two randomized, controlled, open-label, multicenter trials in treatment-experienced subjects, T20-301 (TORO 1) and T20-302 (TORO 2).

Local Injection Site Reactions

Local injection site reactions were the most frequent adverse events associated with the use of FUZEON. In T20-301 and T20-302, 98% of subjects had at least one local injection site reaction (ISR). A total of 7% of subjects discontinued treatment with FUZEON because of ISRs (4%) or difficulties with injecting FUZEON (3%) such as injection fatigue and inconvenience. Eighty-five percent of subjects experienced their first ISR during the initial week of treatment; ISRs continued to occur throughout treatment with FUZEON. For most subjects the severity of signs and symptoms associated with ISRs did not change during the 48 weeks of treatment. The majority of ISRs were associated with erythema, induration, the presence of nodules or cysts, and mild to moderate pain at the injection site (Table 2). In addition, the average duration of individual ISRs was between three and seven days in 41% of subjects and more than seven days in 24% of subjects. Also, the numbers of ISRs per subject at any one time was between six to 14 ISRs in 26% of subjects and more than 14 ISRs in 1.3% of subjects. Infection at the injection site (including abscess and cellulitis) was reported in 1.7% of adult subjects.

Table 2 : Summary of Individual Signs/Symptoms Characterizing Local Injection Site Reactions to Enfuvirtide in Studies T20-301 and T20-302 Combined (% of Subjects) Through 48 Weeks

Event Category N=663
Any Severity Grade % of Subjects with Grade 3 Reactions % of Subjects with Grade 4 Reactions
Pain/Discomforta 96% 11% 0%
Induration 90% 39% 18%
>25 but <50 mm ≥50 mm
Erythema 91% 22% 10%
>50 but <85 mm >85 mm
Nodules and Cysts 80% 23% 0.2%
>3 cm average diameter Draining
Pruritusb 65% 3% NA
Ecchymosis 52% 5% 2%
>3 but ≤5 cm >5 cm
aGrade 3 = severe pain requiring prescription non-topical analgesics or limiting usual activities.
Grade 4 = severe pain requiring hospitalization or prolongation of hospitalization, resulting in death, or persistent or significant disability/incapacity, or life-threatening, or medically significant.
bGrade 3 = refractory to topical treatment or requiring oral or parenteral treatment.
Grade 4 = not applicable.

Other Adverse Events

In T20-301 and T20-302, after study week 8, subjects on background alone who met protocol defined criteria for virological failure were permitted to revise their background regimens and add FUZEON. Exposure on FUZEON+background was 557 patient-years, and to background alone 162 patient-years. Due to this difference in exposure, safety results are expressed as the number of patients with an adverse event per 100 patient-years of exposure. For FUZEON+background, adverse events are also displayed by percent of subjects.

The events most frequently reported in subjects receiving FUZEON+background regimen, excluding ISRs, were diarrhea (38 per 100 patient-years or 31.7%), nausea (27 per 100 patient-years or 22.8%), and fatigue (24 per 100 patient-years or 20.2%). These events were also commonly observed in subjects that received background regimen alone: diarrhea (73 per 100 patient-years), nausea (50 per 100 patient-years), and fatigue (38 per 100 patient-years).

Treatment-emergent adverse events, regardless of causality and excluding ISRs, from Phase 3 studies are summarized for adult subjects, in Table 3. Any Grade 2 or above events occurring at ≥2 percent of subjects and at a higher rate in subjects treated with FUZEON are summarized in Table 3; events that occurred at a higher rate in the control arms are not displayed.

Rates of adverse events for subjects who switched to FUZEON after virological failure were similar.

Table 3 : Rates of Treatment-Emergent Adverse Events* (≥Grade 2) Reported in ≥2% of Subjects Treated with FUZEON** (Pooled Studies T20-301/T20-302 at 48 Weeks)

Adverse Event (by System Organ Class) FUZEON+ Background Regimen
FUZEON+ Background Regimen
Background Regimen
663 subjects total 557 total patient-years 162 total patient-years
% frequency rate/100 patient-years rate/100 patient-years
Weight Decreased 6.6% 7.9 6.2
Sinusitis 6.0% 7.2 4.9
Abdominal Pain 3.9% 4.7 3.7
Cough 3.9% 4.7 2.5
Herpes Simplex 3.5% 4.1 3.7
Appetite Decreased 3.2% 3.8 2.5
Pancreatitis 3.0% 3.6 2.5
Pain in Limb 2.9% 3.4 3.1
Pneumonia (see text below) 2.7% 3.2 0.6
Myalgia 2.7% 3.2 1.2
Influenza-Like Illness 2.4% 2.9 1.9
Folliculitis 2.4% 2.9 2.5
Anorexia 2.3% 2.7 1.9
Dry Mouth 2.1% 2.5 1.9
Conjunctivitis 2.0% 2.3 1.9
*Excludes Injection Site Reactions
**Events listed occurred more frequently in subjects treated with FUZEON (based on rates/100 patient-years).

Less Common Events

The following adverse events have been reported in 1 or more subjects; however, a causal relationship to FUZEON has not been established.

Immune System Disorders: worsening abacavir hypersensitivity reaction

Renal and Urinary Disorders: glomerulonephritis; tubular necrosis; renal insufficiency; renal failure (including fatal cases)

Blood and Lymphatic Disorders: thrombocytopenia; neutropenia; fever; lymphadenopathy

Endocrine and Metabolic: hyperglycemia

Infections: sepsis; herpes simplex

Nervous System Disorders: taste disturbance; Guillain-Barre syndrome (fatal); sixth nerve palsy; peripheral neuropathy

Cardiac Disorders: unstable angina pectoris

Gastrointestinal Disorders: constipation; abdominal pain upper

General: asthenia

Hepatobiliary Disorders: toxic hepatitis; hepatic steatosis

Investigations: increased amylase; increased lipase; increased AST; increased GGT; increased triglycerides

Psychiatric Disorders: insomnia; depression; anxiety; suicide attempt

Respiratory, Thoracic, and Mediastinal Disorders: pneumopathy; respiratory distress; cough

Skin and Subcutaneous Tissue Disorders: pruritus

Laboratory Abnormalities

Table 4 shows the treatment-emergent laboratory abnormalities that occurred in at least 2 subjects per 100 patient-years and more frequently in those receiving FUZEON+background regimen than background regimen alone from T20-301 and T20 302.

Table 4 : Treatment-Emergent Laboratory Abnormalities in ≥2% of Subjects Receiving FUZEON* (Pooled Studies T20-301 and T20-302 at 48 Weeks)

Laboratory Parameters Grading FUZEON+ Background Regimen (N=663) FUZEON+ Background Regimen
Background Regimen
663 subjects total 557 total patient-years 162 total patient-years
% frequency rate/100 patient-years rate/100 patient-years
1-2 X ULN (0.7 x 109/L) 0.7-1.4 x 109/L 9.1% 10.8 3.7
>2 X ULN (0.7 x 109/L) >1.4 x 109/L 1.8% 2.2 1.8
Grade 3 >5-10 x ULN 4.1% 4.8 4.3
Grade 4 >10 x ULN 1.2% 1.4 1.2
Creatine Phosphokinase (U/L)
Grade 3 >5-10 x ULN 6.9% 8.3 8.0
Grade 4 >10 x ULN 2.6% 3.1 8.6
*Events listed occurred more frequently in subjects treated with FUZEON (based on rates/100 patient-years).

Adverse Events In Pediatric Patients

FUZEON has been studied in 63 pediatric subjects 5 through 16 years of age with duration of FUZEON exposure ranging from 1 dose to 134 weeks. Adverse experiences seen during clinical trials were similar to those observed in adult subjects, although infections at site of injection (cellulitis or abscess) were more frequent in adolescents than in adults, with 4 events occurring in 3 of 28 (11%) subjects.

Postmarketing Experience

The following adverse reaction has been identified during post approval use of FUZEON. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Skin And Subcutaneous Tissue Disorders

Cutaneous amyloidosis at the injection site.

Read the entire FDA prescribing information for Fuzeon (Enfuvirtide)

© Fuzeon Patient Information is supplied by Cerner Multum, Inc. and Fuzeon Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

Health Solutions From Our Sponsors