Infergen Side Effects Center

Last updated on RxList: 3/1/2022
Infergen Side Effects Center

What Is Infergen?

Infergen (interferon alfacon-1) is a synthetic type-I interferon made from human proteins and is used to treat chronic hepatitis C.

What Are Side Effects of Infergen?

Common side effects of Infergen include:

  • mood changes
  • irritability
  • nervousness
  • anxiety
  • headache
  • tiredness
  • numbness/tingling/pain in hands or feet
  • joint or muscle pain
  • back pain
  • stomach pain
  • nausea
  • diarrhea
  • weight loss, or
  • thinning hair

Dosage for Infergen

The recommended dose of Infergen when used alone is 15 mcg administered three times a week as a single subcutaneous injection for up to 48 weeks.

What Drugs, Substances, or Supplements Interact with Infergen?

Infergen may interact with drugs that weaken your immune system, such as: cancer medicine, steroids, medicines used to prevent organ transplant rejection, or medicines to treat autoimmune disorders such as arthritis, psoriasis, ulcerative colitis, or Crohn's disease. Tell your doctor all medications and supplements you use.

Infergen During Pregnancy or Breastfeeding

During pregnancy, Infergen should be used only if prescribed. Infergen is sometimes used together with another drug called ribavirin. Ribavirin can cause birth defects or death in a fetus. Consult your doctor for details if you are taking ribavirin along with Infergen. It is unknown if this drug passes into breast milk or if it could harm a nursing baby. Consult your doctor before breastfeeding.

Additional Information

Our Infergen (interferon alfacon-1) 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.


Hepatitis C virus causes an infection of the ______________. See Answer
Infergen Consumer Information

Get emergency medical help if you have signs of an allergic reaction (hives, itching, anxiety, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning eyes, skin pain, red or purple skin rash with blistering and peeling).

Interferon beta-1a can cause life-threatening blood clots in the small blood vessels inside your organs, such as your brain or kidneys. Seek medical help right away if you have symptoms of this condition, such as a fever, tiredness, decreased urination, bruising, or nosebleeds.

Call your doctor at once if you have:

  • pain, swelling, bruising, redness, oozing, or skin changes where the injection was given;
  • a light-headed feeling, like you might pass out;
  • unusual changes in mood or behavior (feeling hopeless, anxious, nervous, irritable, or depressed);
  • thoughts about suicide or hurting yourself;
  • easy bruising, unusual bleeding;
  • a seizure;
  • heart problems--swelling, rapid weight gain, feeling short of breath, rapid heartbeats, chest pain spreading to your jaw or shoulder, nausea, sweating;
  • liver problems--nausea, loss of appetite, tiredness, confusion, easy bruising or bleeding, dark urine, clay-colored stools, or jaundice (yellowing of your skin or eyes);
  • signs of infection--fever, chills, cough with mucus, bloody diarrhea, pain or burning when you urinate; or
  • thyroid problems--mood swings, trouble sleeping, tiredness, hunger, diarrhea, pounding heartbeats, muscle weakness, sweating, dry skin, thinning hair, menstrual changes, weight changes, puffiness in your face, feeling more sensitive to hot or cold temperatures.

Common side effects may include:

  • low blood cell counts;
  • skin changes where the injection was given;
  • depression;
  • abnormal liver function tests;
  • stomach pain; or
  • flu symptoms--headache, fever, chills, chest pain, back pain, tiredness, weakness, muscle aches.

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 Infergen (Interferon Alfacon-1)


Hepatitis: How Do You Get Hepatitis A, B, and C? See Slideshow
Infergen Professional Information


INFERGEN alone or in combination with ribavirin causes a broad range of serious adverse reactions [see BOXED WARNING and 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 clinical practice.

During clinical development, more than 560 subjects were exposed to 9 mcg or 15 mcg of INFERGEN monotherapy administered three times per week over a range of 24 to 48 weeks, and more than 480 subjects were exposed to 9 mcg or 15 mcg of INFERGEN, in combination with ribavirin, administered daily up to 48 weeks.

INFERGEN Monotherapy Clinical Trials

Adverse reactions that were reported, regardless of attribution to treatment, in ≥ 10% of subjects in INFERGEN monotherapy studies are presented in Table 4.

Flu-like symptoms (i.e., headache, fatigue, fever, rigors, myalgia, arthralgia, and sweating increased) were the most frequently reported treatment-related adverse reactions. In most cases, these events could be treated symptomatically.

Depression of any severity was reported in 26% of subjects who received 9 mcg INFERGEN monotherapy and was the most common adverse reaction resulting in study drug discontinuation.

INFERGEN 15 mcg three times a week monotherapy as subsequent treatment was associated with a greater incidence of leukopenia and granulocytopenia. One or more dose reductions for any causes were required in up to 36% of subjects.

Table 4: Treatment Emergent Adverse Reactions Occurring in ≥ 10% of Subjects in INFERGEN Monotherapy Trials

  Initial Treatment Subsequent Treatment
(n = 231)
IFN α-2b
(n = 236)
INFERGEN 15 mcg 24 wks
(n = 165)
INFERGEN 15 mcg 48 wks
(n = 168)
Body System/Preferred Term (COSTART) % of Subjects % of Subjects
  Injection Site Erythema 23 15 17 22
  Fatigue 69 67 65 71
  Fever 61 45 58 55
  Rigors 57 45 62 66
  Body Pain 54 45 39 51
  Influenza-like Symptoms 15 11 8 8
  Chest Pain 13 14 5 9
  Hot Flushes 13 7 7 4
  Malaise 11 10 2 5
  Asthenia 9 11 10 7
  Headache 82 83 78 80
  Insomnia 39 30 24 28
  Dizziness 22 25 18 25
  Paresthesia 13 10 9 9
  Hypoesthesia 10 8 8 10
  Amnesia 10 6 2 5
  Abdominal Pain 41 40 24 32
  Nausea 40 36 30 36
  Diarrhea 29 24 24 22
  Anorexia 24 17 21 14
  Dyspepsia 21 18 12 10
  Vomiting 12 11 13 11
  Myalgia 58 56 51 55
  Arthralgia 51 44 43 46
  Back Pain    42 37 29 23
  Limb Pain 26 25 13 23
  Skeletal Pain 14 14 10 12
  Neck Pain 14 13 8 5
  Nervousness 31 29 16 22
  Depression 26 25 18 19
  Anxiety 19 18 9 14
  Emotional Lability 12 11 6 3
  Thinking Abnormal 8 12 10 20
  Pharyngitis 34 31 17 21
  Cough 22 17 12 11
  Sinusitis 17 22 12 16
  Dyspnea 7 12 8 7
  Alopecia 14 25 10 13
  Pruritus 14 14 11 10
  Rash 13 15 13 10
  Sweating Increased 12 11 13 11

Combination Treatment with INFERGEN/Ribavirin Clinical Trials

The most common adverse reactions in the combination treatment with INFERGEN/ribavirin trial are listed in Table 5 and included fatigue (76%), nausea (45%), flu-like symptoms (40%), headache (42%), arthralgia (31%), and myalgia (29%), neutropenia (40%), leukopenia (29%), insomnia (39%), and depression (26%).

Adverse reactions led to early study discontinuation in 104 (21%) of subjects; more subjects discontinued from the 15 mcg INFERGEN group (64 versus 40). Fatigue, anemia, and depression were the most common adverse reactions resulting in study drug discontinuation. A higher proportion of subjects who received the recommended starting dose of 15 mcg (52%) than the 9 mcg dose group (40%) required INFERGEN dose modifications due to adverse reactions, primarily due to neutropenia/leukopenia, thrombocytopenia, and fatigue/weakness. A total of 14% of subjects experienced serious adverse reactions, the most common of which were neutropenia (2%), suicidal ideation (1%), and hyperuricemia (1%).

Table 5: Treatment Emergent Adverse Reactions Occurring in the > 10% of Subjects in Combination Treatment with INFERGEN/Ribavirin Phase 3 Trial

INFERGEN 9 mcg/RBV 48 wks
(n = 244)
INFERGEN 15 mcg/RBV 48 wks
(n = 242)
Body System/Preferred Term (MedDRA) % of Subjects
  Abdominal pain 15 14
  Constipation 9 10
  Diarrhea 18 19
  Nausea 45 45
  Vomiting 12 19
  Fatigue    75 77
  Influenza-like Illness (or Symptoms) 40 42
  Injection Site Erythema 16 16
  Injection Site Reaction 15 12
  Pyrexia (or Fever) 13 17
  Rigors 19 22
  Weight Decrease 16 22
  Anorexia 15 21
  Decreased appetite 17 18
  Arthralgia 31 31
  Back Pain 12 9
  Myalgia 24 34
  Dizziness 14 19
  Headache 46 39
  Anxiety    12 11
  Depression    27 25
  Insomnia 39 38
  Irritability 21 17
  Cough 14 17
  Dyspnea 15 20
  Alopecia 10 10
  Pruritus 15 11
  Rash 17 12

Laboratory Values

Hemoglobin and Hematocrit: Treatment with INFERGEN alone and in combination with ribavirin is associated with decreases in mean values for hemoglobin and hematocrit. In the INFERGEN monotherapy trials, 4% and 5% of subjects had decreases in hemoglobin and hematocrit levels. Decreases from baseline of 20% or more in hemoglobin or hematocrit were seen in ≤ 1% of subjects.

In the combination INFERGEN/ribavirin trial, 88% of subjects had decreases in hemoglobin levels of ≥ 2 g/dL from baseline. Of these, 27% had hemoglobin levels decrease to ≤ 10 g/dL, and underwent dose reductions of ribavirin. Anemia or hemolytic anemia led to study drug discontinuation in 10 subjects.

White Blood Cells: INFERGEN treatment is associated with decreases in mean values for both total white blood cell (WBC) count and ANC. By the end of initial monotherapy treatment, mean decreases from baseline of 19% for WBCs and 23% for ANC were observed. These effects reversed during the post treatment observation period. In two INFERGEN-monotherapy treated subjects ANC levels decreased to below 500 × 106 cells/L. In both cases, the ANC values returned to clinically acceptable levels with INFERGEN dose reductions and were not associated with infections.

Mean decreases from baseline up to 23% for WBCs and up to 27% for ANC were observed for subjects subsequently retreated with INFERGEN monotherapy. Two subjects experienced reversible reductions in ANC to less than 500 × 106 cells/L.

In the combination INFERGEN/ribavirin trial, leukopenia was reported in 24% and 34% of 9 mcg and 15 mcg treated subjects, respectively. More subjects treated with 15 mcg experienced lymphopenia than did those treated with 9 mcg: 14% versus 7%. ANC levels < 0.75 x 109/L were observed in 21% of subjects treated with 9 mcg and 27% of those treated with 15 mcg; no subjects experienced significant infections associated with low ANC levels.

Platelets: INFERGEN treatment is associated with alterations in platelet count. Decreases in mean platelet count of 16% compared to baseline were seen by the end of INFERGEN monotherapy treatment. These decreases were reversed during the post treatment observation period. Three percent of subjects had platelets decrease to less than 50 × 109 cells/L, which necessitated dose reduction.

More subjects treated with 15 mcg in the INFERGEN/ribavirin combination trial experienced a decrease in platelet counts < 40 × 109/L, 3% versus 1% in the 9 mcg dose group. None of the subjects had platelet counts < 25 × 109/L. One subject in the 15 mcg group had Grade 4 thrombocytopenia 127 days after the start of treatment, was hospitalized for this event, and treatment with both study drugs was discontinued; the event resolved 8 days later.

Triglycerides: Mean values for serum triglyceride increased shortly after the start of administration of INFERGEN monotherapy, with increases of 41%, compared with baseline, at the end of the treatment period. Seven percent of the subjects developed values which were at least 3 times above pretreatment levels during treatment. This effect was reversed after discontinuation of treatment.

In the INFERGEN/ribavirin combination trial, 7% of subjects in the 15 mcg dose group experienced increases in triglyceride levels over baseline levels at week 48 compared to 2% in the 9 mcg dose group. There were no differences in the proportion of subjects who had ≥ Grade 3 triglyceride elevations: 2% in both dose groups.

Thyroid Function: INFERGEN monotherapy treatment was associated with biochemical changes consistent with hypothyroidism including increases in TSH and decreases in T4 mean values. Increases in TSH to greater than 7 mU/L were seen in 10% of 9 mcg INFERGEN-treated subjects either during the treatment period or the 24-week post treatment observation period. Thyroid supplements were instituted in approximately one-third of these subjects.

In the combination INFERGEN/Ribavirin trial, mean increases in TSH levels from baseline were greater for the 15 mcg group compared with the 9 mcg group; 14% and 3%, respectively, at Week 12 and 54% and 0% at Week 48. No serious adverse events, discontinuations or dose modifications were related to abnormalities in thyroid function.

Uric Acid: Grade 4 ( > 10 mg/dL) uric acid levels were commonly observed in both INFERGEN/ribavirin treatment groups: 23 in the 9 mcg and 26 in the 15 mcg group. One subject in the 9 mcg group and three in the 15 mcg group experienced serious adverse events related to elevated uric acid levels. Four subjects in the 15 mcg had INFERGEN/ribavirin temporarily interrupted due to elevated uric acid levels.


The number of subjects developing positive binding antibody responses was similar in the 9 mcg INFERGEN (11%) and 3 MIU IFN α-2b groups (15%) in monotherapy studies. The titer of neutralizing antibodies to interferon was not measured. Following cessation of interferon therapy, the number of subjects with a positive antibody response declined.

In the INFERGEN/ribavirin combination study, approximately 13% of subjects in the 15 mcg and 18% in the 9 mcg arms developed low-titer neutralizing antibodies to INFERGEN. The clinical and pathological significance of the appearance of serum neutralizing antibodies is unknown. No apparent correlation of antibody development to clinical response was observed. The incidence of binding antibody was approximately 31%.

The detection of antibody formation is highly dependent on the sensitivity and specificity of the assay. Additionally, the observed incidence of antibody (including neutralizing antibody) positivity in an assay may be influenced by several factors including assay methodology, sample handling, timing of sample collection, concomitant medications, and underlying disease. For these reasons, comparison of the incidence of antibodies for INFERGEN with the incidence of antibodies to other products may be misleading.

Postmarketing Experience

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

Application site

injection site reaction, including injection site necrosis ulcer, and bruising

Ear and Labyrinth

hearing loss, hearing impairment


abdominal distention, gastrointestinal bleeding, gastritis


hepatic enzyme elevations, including ALT and AST elevation, abnormal hepatic function, hyperbilirubinemia, jaundice, ascites, hepatic encephalopathy



Metabolism and Nutritional



rhabdomyolysis, arthritis, bone pain


speech disorder, ataxia, gait abnormal, convulsions, loss of consciousness, memory impairment, tremors, visual field defect


delusions, hallucinations

Skin and Subcutaneous

bruising, pyoderma gangrenosum, toxic epidermal necrolysis

Vascular Disorders


Read the entire FDA prescribing information for Infergen (Interferon Alfacon-1)

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

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