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Intron A Side Effects

Generic Name: interferon alfa-2b

Note: This page contains information about the side effects of interferon alfa-2b. Some of the dosage forms included on this document may not apply to the brand name Intron A.

Not all side effects for Intron A may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to interferon alfa-2b: injection kit, injection powder for solution, injection solution

In addition to its needed effects, some unwanted effects may be caused by interferon alfa-2b (the active ingredient contained in Intron A). In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking interferon alfa-2b:

More common
  • Depression
  • difficult or labored breathing
  • swelling or puffiness of the face
  • tightness in the chest
  • weight loss
Less common
  • Back, leg, or stomach pains
  • bleeding, tender, or enlarged gums
  • bloody, black, or tarry stools
  • bloody nose
  • bloody or cloudy urine
  • blurred vision
  • change in personality
  • changes in behavior
  • chest pain, discomfort, or heaviness
  • chills
  • clay-colored stools
  • confusion as to time, place, or person
  • constipation
  • cough producing mucus
  • coughing or spitting up blood
  • dark urine
  • decreased urination
  • diarrhea
  • difficult or painful urination
  • dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
  • drowsiness
  • fainting
  • fast, slow, pounding, irregular, or racing heartbeat or pulse
  • feeling, seeing, or hearing things that are not there
  • feeling that others are watching you or controlling your behavior
  • feeling that others can hear your thoughts
  • fever
  • hallucinations
  • headache
  • hearing loss
  • heavier menstrual periods
  • hives
  • hoarseness or husky voice
  • inability to speak
  • increased thirst
  • increased urination
  • indigestion
  • irritability
  • itching, pain, redness, or swelling of the skin
  • light-colored stools
  • lightheadedness
  • loss of appetite
  • loss of consciousness
  • loss of hearing
  • lower back or side pain
  • metallic taste
  • muscle aches or cramps
  • nausea or vomiting
  • pale skin
  • passing of gas
  • pinpoint red spots on the skin
  • rash
  • seizures
  • severe mood or mental changes
  • severe stomach pain with nausea and vomiting
  • skin rash
  • slow speech
  • sneezing
  • sores, ulcers, or white spots on the lips or tongue or inside the mouth
  • stiffness of the limbs
  • stomach cramps, tenderness, or discomfort
  • stomach pain, continuing
  • stomach upset
  • sweating
  • swelling around the eyes
  • swelling of the face, fingers, hands, ankles, feet, or lower legs
  • swollen, painful, or tender lymph glands in the neck, armpit, or groin
  • thoughts of hurting or killing oneself
  • trouble sleeping
  • unusual behavior
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • weight gain
  • yellowing of the eyes or skin

Some of the side effects that can occur with interferon alfa-2b may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common
  • Acid or sour stomach
  • bleeding gums
  • blistering, crusting, irritation, itching, or reddening of the skin
  • body aches or pain
  • burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
  • change in taste, or bad, unusual, or unpleasant (after) taste
  • cracked, dry, or scaly skin
  • hair loss or thinning of the hair
  • irritation in the mouth
  • joint pain
  • lack or loss of strength
  • loss of memory
  • muscle or bone pain
  • pain or tenderness around the eyes and cheekbones
  • poor concentration
  • problems with memory
  • redness and swelling of the gums
  • stuffy or runny nose
  • swollen joints
Less common
  • Abnormal ejaculation
  • absent, missed, or irregular menstrual periods
  • bleeding, burning, inflammation, itching, or pain at the injection site
  • bone deformity
  • burning, itching, and pain in the hairy areas, pus at the root of the hair
  • burning, numbness, pain, or tingling in all fingers except smallest finger
  • cold and clammy skin
  • decrease in height
  • decreased interest in sexual intercourse
  • degenerative disease of the joint
  • difficulty with moving or walking
  • discoloration of the skin
  • inability to have or keep an erection
  • increased clear or white vaginal discharge
  • increased sensitivity of the skin to sunlight
  • itching or pain of the genital area
  • leg cramps
  • longer menstrual periods
  • loss in sexual ability, desire, drive, or performance
  • multiple swollen and inflamed skin lesions
  • pain in the ankles or knees
  • pain in the ribs
  • pain, inflammation, or swelling in the calves, shoulders, or hands
  • painful, red lumps under the skin, mostly on the legs
  • pelvic pain
  • rash with flat lesions or small raised lesions on the skin
  • red or irritated eyes
  • redness or swelling in the arms or legs
  • redness, tenderness, itching, burning, or peeling of the skin
  • severe sunburn
  • shivering
  • skin rash, encrusted, scaly, and oozing small lumps under the skin
  • small lumps under the skin
  • soreness of the muscles
  • stopping of menstrual bleeding
  • swelling or redness in the joints
  • tanning or blue-gray discoloration of the skin
  • tearing of the eyes
  • underactive reflexes
  • unexpected menstrual bleeding

For Healthcare Professionals

Applies to interferon alfa-2b: injectable kit, injectable powder for injection, injectable solution


Most side effects reported during clinical trials were mild to moderate in severity and manageable. Some side effects were transient and most diminished with continued treatment. "Influenza-like" symptoms (mainly fever, headache, chills, myalgia, and fatigue) were reported most often. In general, more severe toxicities were observed at higher doses.


Gastrointestinal side effects have included anorexia (up to 69%), nausea (up to 66%), diarrhea (up to 45%), vomiting (up to 32%), altered taste (up to 24%), abdominal pain (up to 23%), constipation (up to 14%), gingivitis (up to 14%), loose stools (up to 10%), dyspepsia (up to 7%), and gastrointestinal disorder (up to 7%). Abdominal ascites, abdominal distension, colitis, dysphagia, eructation, esophagitis, flatulence, gallstones, gastric ulcer, gastritis, gastroenteritis, gastrointestinal hemorrhage, gastrointestinal mucosal discoloration, gingival bleeding, gum hyperplasia, halitosis, hemorrhoids, increased appetite, increased saliva, intestinal disorder, melena, mouth ulceration, mucositis, oral hemorrhage, oral leukoplakia, rectal bleeding after stool, rectal hemorrhage, stomatitis, stomatitis ulcerative, taste loss, tongue disorder, and tooth disorder have been reported in less than 5% of patients. Pancreatitis has also been reported during postmarketing experience.[Ref]


Hepatic side effects have included elevated SGOT (up to 63%) and right upper quadrant pain (up to 15%). Abnormal hepatic function tests, biliary pain, bilirubinemia, hepatitis, increased lactate dehydrogenase, increased transaminases (SGOT/SGPT), and jaundice have been reported in less than 5% of patients. Hepatic encephalopathy, hepatic failure, and death have been reported very rarely.[Ref]


Psychiatric side effects have included depression (up to 40%), anxiety (up to 9%), and nervousness (up to 3%). Abnormal dreaming, aggravated depression, aggressive reaction, apathy, emotional lability, feeling of ebriety, manic depression, manic reaction, personality disorder, psychosis, suicidal ideation, and suicide attempt have been reported in less than 5% of patients. Frontal subcortical dementia and choreic movements mimicking Huntington's disease have been reported. Homicidal ideation and psychosis including hallucinations have been reported during postmarketing experience.[Ref]

Frontal subcortical dysfunction and choreic movements of the limbs appeared in a 68-year-old woman almost 2 years after the initiation of interferon alfa-2b (3 x 10(6) units/day) for CML. She had no history of psychiatric disorders and no hereditary neurodegenerative disease with long term recombinant interferon therapy. Symptoms of personality changes, short memory loss, and choreic movements progressively worsened over a 4 months period until she became bedridden. One month after interferon alfa-2b therapy was discontinued patient's cognitive performance had improved and choreic movements had disappeared. Clinical examination of her cognitive performances at six and 12 months later were normal.[Ref]


Case reports of aseptic necrosis of the skin and ulceration have been described in patients with Kaposi's sarcoma associated with HIV infection treated with interferon alfa-2b (the active ingredient contained in Intron A) [Ref]

Dermatologic side effects have included alopecia (up to 38%), rash (up to 25%), pruritus (up to 11%), dry skin (up to 10%), dermatitis (up to 8%), and hair discoloration. Abnormal hair texture, acne, cellulitis, dermatitis lichenoides, eczema, epidermal necrolysis, erythema, erythema nodosum, folliculitis, furunculosis, increased hair growth, lipoma, maculopapular rash, melanosis, nail disorders, nonherpetic cold sores, pallor, photosensitivity, psoriasis, aggravated psoriasis, erythematous rash, sebaceous cyst, skin depigmentation, skin discoloration, skin nodule, urticaria, and vitiligo have been reported in less than 5% of patients. Trichomegaly following treatment with interferon alfa-2b has been reported in a few cases, but mechanism is unknown. Radiation recall dermatitis manifested as an erythematous macular rash in the region of irradiation has been reported after a high-dose of interferon alfa-2b. Aseptic necrosis of the skin and ulceration have been reported. Erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis, and urticaria have been reported during postmarketing experience.[Ref]


Respiratory side effects have included dyspnea (up to 34%), coughing (up to 31%), pharyngitis (up to 31%), sinusitis (up to 21%), nonproductive cough (up to 14%), nasal congestion (up to 10%), and bronchitis (up to 10%). Asthma, bronchospasm, cyanosis, epistaxis, hemoptysis, hypoventilation, laryngitis, lung fibrosis, pleural effusion, orthopnea, pleural pain, pneumonia, pneumonitis, pneumothorax, rales, respiratory disorder, respiratory insufficiency, sneezing, tonsillitis, tracheitis, and wheezing have been reported in up to 5% of patients. Rhinitis and rhinorrhea have been reported in less than 5% of patients. Pulmonary hypertension and at least two cases of severe asthma have been reported during postmarketing experience.[Ref]

Severe asthma developed in two patients as soon as 8 weeks after the start of interferon alfa-2b therapy in patients diagnosed with chronic hepatitis C and mild asthma.[Ref]

Nervous system

Nervous system side effects have included headache (up to 62%), somnolence (up to 33%), dizziness (up to 24%), irritability (up to 22%), paresthesia (up to 21%), impaired concentration (up to 14%), amnesia (up to 14%), confusion (up to 12%), insomnia (up to 12%), hypoesthesia (up to 10%), vertigo (up to 8%), and decreased libido (up to 5%). Abnormal coordination, abnormal gait, abnormal thinking, agitation, alcohol intolerance, aphasia, ataxia, Bell's palsy, central nervous system dysfunction, coma, convulsions, delirium, dysphonia, extrapyramidal disorder, hearing impairment, hyperesthesia, hyperkinesias, hypertonia, hypokinesia, impaired consciousness, labyrinthine disorder, loss of consciousness, migraine, neuralgia, neuritis, neuropathy, neurosis, paresis, paroniria, parosmia, polyneuropathy, speech disorder, stroke, syncope, tinnitus, tremor, and twitching have been reported in less than 5% of patients. Peripheral neuropathy and hearing loss have been reported during postmarketing experience.[Ref]


Musculoskeletal side effects have included myalgia (up to 75%), musculoskeletal pain (up to 21%), and arthralgia (up to 19%). Arteritis, arthritis, aggravated arthritis, arthrosis, bone disorder, bone pain, carpal tunnel syndrome, hyporeflexia, leg cramps, muscle atrophy, muscle weakness, polyarteritis nodosa, tendinitis, rheumatoid arthritis, and spondylitis have been reported in less than 5% of patients. Myositis has been reported during postmarketing experience.[Ref]


Immunologic side effects have included moniliasis (up to 17%), nonspecific infection (up to 7%), viral infection (up to 7%), and herpes simplex (up to 5%). Other resistance mechanism disorders have been reported in less than 5% of patients and have included abscess, conjunctivitis, fungal infection, hemophilus, herpes zoster, infection, bacterial infection, parasitic infection, otitis media, sepsis, stye, trichomonas, and upper respiratory tract infection. Systemic lupus erythematosus has been reported during postmarketing experience.[Ref]


Hematologic side effects have included neutropenia (up to 92%), anemia (up to 22%), thrombocytopenia (up to 10%), bleeding (up to 8%), and purpura (up to 5%). Hypochromic anemia, granulocytopenia, hemolytic anemia, leukopenia, lymphadenitis, lymphadenopathy, lymphocytosis, poor peripheral circulation, and thrombocytopenia purpura have been reported in less than 5% of patients. Aplastic anemia, pure red cell aplasia, pancytopenia (concurrent anemia, leukopenia, thrombocytopenia), sarcoidosis or exacerbation of sarcoidosis, idiopathic thrombocytopenia purpura, and thrombotic thrombocytopenic purpura have been reported during postmarketing experience.[Ref]


Genitourinary side effects have included amenorrhea (up to 12%) and polyuria (up to 10%). Mastitis, scrotal/penile edema, and urinary tract infections have been reported in up to 5% of patients. Albumin/protein in urine, cystitis, dysmenorrhea, dysuria, hematuria, impotence, incontinence, leukorrhea, menorrhagia, menstrual irregularity, micturition disorder, micturition frequency, nocturia, pelvic pain, penis disorder, sexual dysfunction, uterine bleeding, vaginal dryness, and gynecomastia have been reported in less than 5% of patients.[Ref]


Cardiovascular side effects have included hypertension (up to 9%). Angina, arrhythmia, atrial fibrillation, bradycardia, cardiac failure, cardiomegaly, cardiomyopathy, coronary artery disorder, extrasystoles, heart valve disorder, hematoma, hypotension, palpitations, phlebitis, postural hypotension, pulmonary embolism, Raynaud's disease, tachycardia, thrombosis, and varicose vein have been reported in less than 5% of patients.[Ref]


Endocrine side effects have included aggravation of diabetes mellitus, goiter, hyperthyroidism, and hypothyroidism in less than 5% of patients. Hypopituitarism has been reported during postmarketing experience.[Ref]


Metabolic side effects have included dehydration, hypercalcemia, hyperglycemia, and hypertriglyceridemia in up to 5% of patients. Lipoatrophy has been reported in at least one patient.[Ref]

Elevated triglyceride levels should be managed as clinically appropriate. Severe hypertriglyceridemia (greater than 1000 mg/dL) may result in pancreatitis.[Ref]


Ocular side effects have included abnormal vision, blurred vision, diplopia, dry eyes, eye pain, lacrimal gland disorder, lacrimation, nystagmus, and photophobia in less than 5% of patients. At least seven cases of retinopathy in patients receiving high dose interferon alfa-2b (the active ingredient contained in Intron A) have been reported. Vogt-Koyanagi-Harada syndrome and serous retinal detachment have been reported during postmarketing experience.[Ref]


Renal side effects have included increased BUN and renal insufficiency in less than 5% of patients. Nephrotic syndrome, renal failure, and renal insufficiency have been reported during postmarketing experience.


Hypersensitivity side effects have included allergic reaction (up to 5%). Cases of acute hypersensitivity reactions (including anaphylaxis and angioedema) have been reported during postmarketing experience.


Local side effects have included injection site inflammation (up to 20%). Other application site disorders have been reported in up to 5% of patients and have included burning, injection site bleeding, injection site pain, injection site reaction, and itching. Injection site necrosis has been reported during postmarketing experience.[Ref]


Other side effects have included fatigue (up to 96%), fever (up to 94%), influenza-like symptoms (up to 79%), asthenia (up to 63%), chills (up to 54%), rigors (up to 42%), dry mouth (up to 28%), chest pain (up to 28%), increased sweating (up to 21%), back pain (up to 19%), unspecified pain (up to 18%), malaise (up to 14%), facial edema (up to 10%), decreased weight (up to 13%), and peripheral edema (up to 6%). Cachexia, earache, hernia, edema, hypothermia, nonspecific inflammation, periorbital edema, superficial phlebitis, thirst, weakness, and increased weight have been reported in up to 5% of patients. Substernal chest pain, cyanosis of the hand, cold and clammy skin, flushing, hot flashes, hyperthermia, peripheral ischemia, and virilism have been reported in less than 5% of patients. Asthenic conditions (including asthenia, malaise, fatigue) have been reported during postmarketing experience.[Ref]


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2. "Product Information. Intron A (interferon alfa-2b)." Schering Laboratories, Kenilworth, NJ.

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15. Hamnvik OP, Larsen PR, Marqusee E "Thyroid dysfunction from antineoplastic agents." J Natl Cancer Inst 103 (2011): 1572-87

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