Zanamivir

Pronunciation: za-NAM-i-vir
Class: Antiviral agent

Trade Names

Relenza
- Powder, oral inhalation 5 mg

Pharmacology

Inhibition of influenza virus neuraminidase, with the possibility of alteration of virus particle aggregation and release.

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Pharmacokinetics

Absorption

Approximately 4% to 17% of orally inhaled dose is systemically absorbed. C _max is 17 to 142 ng/mL, and T _max is 1 to 2 h following a 10 mg dose. The AUC is 111 to 1,364 ng•h/mL.

Distribution

Less than 10% protein bound.

Metabolism

No metabolites were detected in humans.

Elimination

Renally excreted as unchanged drug in urine. Serum half-life is 2.5 to 5.1 h. Total Cl is 2.5 to 10.9 L/h. Unabsorbed drug is excreted in feces.

Special Populations

Renal Cl is decreased and the half-life is increased in patients with mild, moderate, or severe renal impairment. Safety and efficacy have not been documented in severe renal insufficiency.

Pharmacokinetics have not been studied in patients with hepatic impairment.

Pharmacokinetics have not been studied in patients older than 65 y.

After a single dose of zanamivir 10 mg inhalation, 5 patients 6 to 12 y of age had undetectable zanamivir serum concentrations or low drug concentrations (8.32 to 10.38 ng/mL) that were not detectable after 1.5 hours, and 11 patients had C _max median values of 43 ng/mL (range, 15 to 74 ng/mL) and AUC _∞ median values of 167 ng•h/mL (range, 58 to 279 ng/mL).

No differences in plasma concentrations or pharmacokinetics were observed between men and women.

No differences in plasma concentrations or pharmacokinetics were observed based on race.

No significant differences in serum concentrations and/or pharmacokinetic parameters were observed.

Indications and Usage

Treatment of uncomplicated acute illness caused by influenza A and B virus in adults and pediatric patients 7 y and older who have been symptomatic for no longer than 2 days; prophylaxis of influenza in adults and pediatric patients 5 y and older.

Contraindications

History of allergic reaction to any ingredient of zanamivir, including lactose (which contains milk proteins).

Dosage and Administration

Oral inhalation 2 inhalations (one 5 mg blister per inhalation) once daily for 28 days.

Oral inhalation 2 inhalations (one 5 mg blister per inhalation) once daily for 10 days.

Oral inhalation 2 inhalations (one 5 mg blister per inhalation) twice daily for 5 days. Two doses should be taken on the first day of treatment whenever possible, provided there are at least 2 h between doses. On subsequent days, doses should be approximately 12 h apart at approximately the same time each day.

General Advice

• For oral inhalation only with the Diskhaler provided. Not for intranasal inhalation.
• When treating influenza, initiate therapy within 48 h of onset of influenza symptoms.
• For the prophylaxis of influenza, there are no data on the effectiveness of prophylaxis with zanamivir in a household setting when initiated more than 1.5 days after the onset of signs or symptoms in the index case or more than 5 days after the outbreak was identified in the community.
• Administer doses at approximately the same time each day.
• Patients scheduled to use an inhaled bronchodilator at the same time as zanamivir should use their bronchodilator before taking zanamivir.

Storage/Stability

Store between 59° and 86°F. Do not puncture any blister until just before inhaling a dose.

Drug Interactions

Administer more than 2 wk before or 48 h after zanamivir.

Adverse Reactions

Cardiovascular

Arrhythmias, syncope, vasovagal-like episodes (postmarketing).

CNS

Headache (24%); fatigue/malaise (8%); dizziness (2%); delirium (including abnormal behavior, agitation, altered level of consciousness, anxiety, confusion, delusions, hallucinations, and nightmares), seizures (postmarketing).

Dermatologic

Urticaria (less than 2%); facial edema, rash (including serious cutaneous reactions, such as erythema multiforme, Stevens-Johnson syndrome, TEN) (postmarketing).

EENT

Nasal signs and symptoms (20%); throat and tonsil discomfort and pain (19%); ear, nose, and throat infections (5%); nasal inflammation (1%).

GI

Diarrhea, nausea (3%); vomiting (2%); abdominal pain (less than 2%).

Metabolic-Nutritional

Decreased or increased appetite and anorexia (4%).

Musculoskeletal

Muscle pain (8%); musculoskeletal pain (6%); arthralgia and articular rheumatism (2%); arthralgia, myalgia (less than 2%).

Respiratory

Cough (17%); viral respiratory infection (13%); sinusitis (3%); bronchitis (2%); bronchospasm, dyspnea (postmarketing).

Miscellaneous

Fever and/or chills (9%); allergic or allergic-like reactions, including oropharyngeal edema (postmarketing).

Precautions

Pregnancy

Category C .

Lactation

Undetermined.

Children

Safety and efficacy not established in children younger than 7 y for the treatment of influenza; safety and efficacy not established in children younger than 5 y for influenza prophylaxis.

Elderly

Elderly patients may need assistance with use of the device.

Hypersensitivity

Allergic-like reactions, including oropharyngeal edema, serious skin rashes, and anaphylaxis, have been reported.

Renal Function

Consider the possibility of drug accumulation.

Special Risk Patients

Safety and efficacy not demonstrated in patients with underlying chronic pulmonary disease (severe COPD or asthma); use is not recommended. Safety and efficacy not demonstrated in patients with high-risk underlying medical conditions.

Administration

Zanamivir powder must not be made into an extemporaneous solution for administration by nebulization or mechanical ventilation. There have been reports of hospitalized patients, including a fatal case, where it was reported that the lactose in this formulation obstructed the proper functioning of the equipment.

Bacterial infections

Not established for prophylactic use to prevent complications from serious bacterial infections that may begin with influenza-like symptoms.

Bronchospasm

Serious cases of bronchospasm, including fatalities, have been reported. Discontinue use if this occurs.

Neuropsychiatric events

Delirium and abnormal behavior leading to injury have been reported in postmarketing experience.

Overdosage

Symptoms

No reports of overdosage.

Patient Information

• Review and demonstrate proper use of the delivery system.
• Advise patients using an inhaled bronchodilator at the same time as zanamivir to use the inhaled bronchodilator before inhaling zanamivir.
• Remind patients to complete entire course of therapy, even if they are feeling better.
• Advise patients that medication does not reduce risk of transmission of flu virus to others, and to continue to take appropriate precautions to prevent spreading the infection.
• Advise patients that zanamivir is not a substitute for flu vaccination and to continue to obtain an annual flu vaccination.
• Advise patients to inform their health care provider if flu symptoms do not appear to be improving or are worsening, or if new symptoms develop during or after treatment.
• Advise patients of the risk of bronchospasm and instruct them to discontinue therapy and contact their health care provider immediately if they experience increased respiratory symptoms (eg, shortness of breath, worsening wheezing).
• Inform patients, particularly children and adolescents, that they may be at an increased risk of seizures, confusion, or abnormal behavior early in their illness. These reactions may occur after beginning zanamivir or when flu is not treated. These reactions are uncommon but may result in accidental injury to the patient. Therefore, observe patients for signs of unusual behavior and a health care provider should be contacted immediately if there are any signs of unusual behavior.

Copyright © 2009 Wolters Kluwer Health.