Skip to main content

Zanamivir Side Effects

Medically reviewed by Last updated on Nov 27, 2022.

Applies to zanamivir: inhalation disk.

Serious side effects of Zanamivir

Along with its needed effects, zanamivir may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking zanamivir:


  • Convulsions
  • dizziness and fainting
  • fast, slow, or irregular heartbeat
  • flushing or reddening of the skin
  • increased sensitivity to sunlight
  • itching, pain, redness, swelling, or watering of the eye or eyelid
  • joint pain
  • severe skin rash or hives
  • shortness of breath or troubled breathing
  • swelling or puffiness of the face
  • swollen glands or tightness in the throat
  • tightness in the chest or wheezing

Other side effects of Zanamivir

Some side effects of zanamivir may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

  • Change in hearing
  • cough
  • cough producing mucus
  • diarrhea
  • dizziness
  • ear drainage
  • ear, nose, and throat infections
  • earache
  • fever or chills
  • headache
  • nasal signs and symptoms
  • nausea
  • pain and pressure over cheeks
  • pain in the ear
  • shortness of breath
  • vomiting

For Healthcare Professionals

Applies to zanamivir: inhalation powder.


In clinical trials, the incidence of adverse events in patients treated with the inhalation powder was similar to that in the placebo (lactose vehicle) group.

The side effects reported most commonly with the IV formulation were elevated ALT, elevated AST, hepatocellular injury, diarrhea, and rash.[Ref]


Inhalation powder:

-Very common (10% or more): Throat/tonsil discomfort/pain (up to 19%), cough (up to 17%), viral respiratory infections (up to 13%), nasal signs/symptoms (up to 12%)

-Common (1% to 10%): Sinusitis, bronchitis, ear/nose/throat infections, nasal inflammation, decline in forced expiratory volume in 1 second (FEV1)

-Frequency not reported: Bronchospasm-like events, congestion, rhinitis, dry throat, ear/nose/throat hemorrhage, asthma, exacerbation of asthma, respiratory arrest, lung tightness, decline in lung function, throat tightness/constriction

-Postmarketing reports: Bronchospasm, dyspnea[Ref]

In a Phase 1 study, bronchospasm was reported in 1 of 13 patients with mild or moderate asthma (but without acute influenza-like illness) after administration of this drug. In a Phase 3 study of patients with acute influenza-like illness and underlying asthma or chronic obstructive pulmonary disease, 24 of 244 patients on this drug (compared to 22 of 237 patients on placebo) experienced greater than 20% decline in FEV1 after 5 days of treatment.

Serious cases of bronchospasm (including fatalities) have been reported during therapy in patients with and without underlying airways disease. Most of these cases were reported during postmarketing experience; causality was difficult to evaluate.[Ref]

Nervous system

Inhalation powder:

-Very common (10% or more): Headaches (up to 24%)

-Common (1% to 10%): Dizziness

-Postmarketing reports: Seizures, syncope, vasovagal-like episodes shortly after inhalation

IV formulation:

-Frequency not reported: Convulsions, depressed level of consciousness[Ref]


Inhalation powder:

-Common (1% to 10%): Malaise/fatigue, temperature regulation disturbances (fever/chills)

-Frequency not reported: Malaise, fatigue, fever

-Postmarketing reports: Facial edema

IV formulation:

-Uncommon (0.1% to 1%): Elevated alkaline phosphatase

-Frequency not reported: Oropharyngeal edema, facial edema[Ref]


Inhalation powder:

-Common (1% to 10%): Muscle pain, musculoskeletal pain, arthralgia/articular rheumatism

-Frequency not reported: Myalgia, arthralgia, elevated creatine phosphokinase[Ref]


Inhalation powder:

-Frequency not reported: Urticaria

-Postmarketing reports: Rash, serious cutaneous reactions (e.g., erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis), urticaria

IV formulation:

-Common (1% to 10%): Rash

-Uncommon (0.1% to 1%): Urticaria

-Frequency not reported: Erythema multiforme, Stevens-Johnson syndrome, toxic epidermal necrolysis[Ref]


Inhalation powder:

-Postmarketing reports: Allergic/allergic-like reactions (including oropharyngeal edema, serious skin rashes, anaphylaxis, anaphylactic/anaphylactoid reactions, facial edema)

IV formulation:

-Frequency not reported: Anaphylactic/anaphylactoid reactions[Ref]


Abnormal behavior and delirium leading to injury, with fatal outcomes in some cases, with the use of this drug in influenza patients have been reported. Although frequency was unknown, based on usage of this drug, these events appeared to be uncommon. These events were primarily reported in pediatric patients and often had an abrupt onset and rapid resolution. Since influenza may be associated with neurologic and behavioral symptoms (including hallucinations, delirium, and abnormal behavior, with fatal outcomes in some cases), contribution of this drug to these events was not established.

Inhalation powder:

-Postmarketing reports: Delirium, altered level of consciousness, confusion, abnormal behavior, delusions, hallucinations, agitation, anxiety, nightmares

IV formulation:

-Frequency not reported: Abnormal behavior, hallucinations, delirium


Inhalation powder:

-Common (1% to 10%): Diarrhea, nausea, vomiting, nausea/vomiting

-Frequency not reported: Abdominal pain

IV formulation:

-Common (1% to 10%): Diarrhea[Ref]


Inhalation powder:

-Common (1% to 10%): Feeding problems (decreased/increased appetite, anorexia)

-Frequency not reported: Hyperkalemia[Ref]


Inhalation powder:

-Frequency not reported: Elevated liver enzymes

IV formulation:

-Common (1% to 10%): Elevated ALT, elevated AST, hepatocellular injury[Ref]


Inhalation powder:

-Frequency not reported: Lymphopenia, neutropenia[Ref]


Inhalation powder:

-Frequency not reported: Hypotension

-Postmarketing reports: Arrhythmias[Ref]


In 1 case report, acute renal failure, increased serum creatinine, hyperkalemia, and hypotension developed in a patient with multiple medical problems and multiple other medications.[Ref]

Inhalation powder:

-Frequency not reported: Acute renal failure, increased serum creatinine[Ref]


1. Product Information. Relenza (zanamivir). Glaxo Wellcome. 2001.

2. Cerner Multum, Inc. UK Summary of Product Characteristics.

3. Cerner Multum, Inc. Australian Product Information.

4. Williamson JC, Pegram PS. Respiratory distress associated with zanamivir. N Engl J Med. 2000;342:661-2.

5. Macdonald L. New influenza drugs zanamivir (Relenza (TM)) and oseltamivir (Tamiflu (TM)): unexpected serious reactions. Can Med Assn J. 2000;163:879-81.

6. Montalto NJ, Gum KD, Ashley JV. Updated treatment for influenza A and B. Am Fam Physician. 2000;62:2467-76.

7. Dreitlein WB, Maratos J, Brocavich J. Zanamivir and oseltamivir: Two new options for the treatment and prevention of influenza. Clin Ther. 2001;23:327-55.

8. Cheer SM, Wagstaff AJ. Zanamivir: an update of its use in influenza. Drugs. 2002;62:71-106.

9. Moscona A. Neuraminidase inhibitors for influenza. N Engl J Med. 2005;353:1363-73.

10. Jefferson T, Demicheli V, Rivetti D, Jones M, Di Pietrantonj C, Rivetti A. Antivirals for influenza in healthy adults: systematic review. Lancet. 2006;367:303-13.

11. Laforce C, Man CY, Henderson FW, et al. Efficacy and safety of inhaled zanamivir in the prevention of influenza in community-dwelling, high-risk adult and adolescent subjects: a 28-day, multicenter, randomized, double-blind, placebo-controlled trial. Clin Ther. 2007;29:1579-1590.

12. McNicholl IR, McNicholl JJ. Neuraminidase inhibitors: zanamivir and oseltamivir. Ann Pharmacother. 2001;35:57-70.

13. Anekthananon T, Pukritayakamee S, Ratanasuwan W, et al. Oseltamivir and inhaled zanamivir as influenza prophylaxis in Thai health workers: a randomized, double-blind, placebo-controlled safety trial over 16 weeks. J Antimicrob Chemother. 2013;68:697-707.

14. Monto AS, Fleming DM, Henry D, et al. Efficacy and safety of the neuraminidase inhibitor zanamivir in the treatment of influenza A and B virus infections. J Infect Dis. 1999;180:254-61.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.