RELENZA
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Pharmacodynamics
Influenza, commonly known as the flu, is caused by a virus which targets the body's respiratory cells and damages the lining of the respiratory tract, leading to swelling and inflammation of the tract. Influenza spreads rapidly by replicating itself inside the host cell, producing hundreds of copies of the virus in a short period. In approximately an hour the virus can destroy the host cell and propel its replications out into the body to find new host cells. For some people, the flu and its complications can be very serious, even fatal.
Zanamivir works by binding to the active site of the neuraminidase protein, rendering the influenza virus unable to escape its host cell and infect others.It is also an inhibitor of influenza virus replication in vitro and in vivo. In clinical trials it was found that zanamivir was able to reduce the time to symptom resolution by 1.5 days if therapy was started within 48 hours of the onset of symptoms.
Pharmacokinetics
The bioavailability of zanamivir is 2 percent. After inhalation, zanamivir is concentrated in the lungs and oropharynx, where up to 15 percent of the dose is absorbed and excreted in urine.
Indications
The treatment of infections caused by Influenzavirus A and Influenzavirus B.
Contraindications
Oral dosing of zanamivir is ineffective, limiting dosing to the inhaled route. This restricts its usage, as treating asthmatics could induce bronchospasm. The FDA has issued a Public Health Advisory warning that it has received some reports of respiratory problems following inhalation of zanamivir by patients with underlying asthma or chronic obstructive pulmonary disease. The zanamivir package insert contains precautionary information regarding risk of bronchospasm in patients with respiratory disease. Do not use in patients with history of allergic reaction to any ingredient of RELENZA including lactose (which contains milk proteins)
Pregnancy and lactation
There are no adequate and well-controlled studies of zanamivir in pregnant women. Zanamivir should be used during pregnancy and in lactation period only if the potential benefit justifies the potential risk to the fetus.
Adverse effects
Zanamivir is specific to the influenza virus, has not been known to cause toxic effects, and does not spread around through the body's systemic circulation. It also shows no signs of viral resistance. However, due to a lack of reports or evidence about its toxicity, the FDA does not license it for use in children under 5 years of age.
DOSAGE AND ADMINISTRATION
RELENZA is for administration to the respiratory tract by oral inhalation only, using the DISKHALER device provided.
- The 10 mg dose is provided by 2 inhalations (one 5 mg blister per inhalation).
Patients scheduled to use an inhaled bronchodilator at the same time as RELENZA should use their bronchodilator before taking RELENZA
The recommended dose of RELENZA for treatment of influenza in adults and pediatric patients 7 years of age and older is 10 mg twice daily (approximately 12 hours apart) for 5 days. - Two doses should be taken on the first day of treatment whenever possible provided there is at least 2 hours between doses.
- On subsequent days, doses should be about 12 hours apart (e.g., morning and evening) at approximately the same time each day.
- The safety and efficacy of repeated treatment courses have not been studied.
The recommended dose of RELENZA for prophylaxis of influenza in adults and pediatric patients 5 years of age and older in a household setting is 10 mg once daily for 10 days. The dose should be administered at approximately the same time each day. There are no data on the effectiveness of prophylaxis with RELENZA in a household setting when initiated more than 1.5 days after the onset of signs or symptoms in the index case.
Importance of Proper Use of DISKHALER
Effective and safe use of RELENZA requires proper use of the DISKHALER to inhale the drug. Prescribers should carefully evaluate the ability of young children to use the delivery system if use of RELENZA is considered
