SAN FRANCISCO - Zanamivir (Relenza, Glaxo Wellcome) may prevent the spread of influenza among family members, according to a study presented here at the 39th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).
"Because it can reduce the transmission of the virus, zanamivir shows promise as a way to curb this common domestic problem," said lead investigator Frederick Hayden, MD, of the University of Virginia Health System, Charlottesville, Va. "Families are an important site for the spread of influenza viruses. Daily interactions of the typical family make it easy for influenza to spread throughout a household."
Results of the double-blind, placebo-controlled clinical trial showed that zanamivir significantly reduced the risk of acquiring influenza by 79%. Out of 337 families, 19% of those who received placebo had one or more members who developed laboratory-confirmed influenza during prophylaxis as compared with only 4% in the group receiving zanamivir.
The trial examined the effectiveness of zanamivir in preventing the spread of influenza types A and B from one infected family member to another. Individuals with influenza-like illness during flu season were randomized to receive either treatment with zanamivir or placebo (10 mg twice daily for five days). The infected patient's healthy family members received the same blinded medication for prevention (10 mg once daily for 10 days).
The age range of study participants was 5 to 72 years. Frequency of side effects were comparable to placebo. The most common side effects for both treatment and prophylaxis included other viral respiratory infections (17% placebo vs. 10% zanamivir), headaches (10% vs. 9%) and nasal signs and symptoms (8% vs. 9%).
Zanamivir is the first inhaled neuraminidase inhibitor to be approved for the treatment of influenza by the Food and Drug Administration (FDA) and will be available in pharmacies for the 1999-2000 flu season. Zanamivir is not indicated for influenza prophylaxis.
Additional research presented at ICAAC showed that zanamivir appeared active against influenza type B, which lacks effective treatment. About 35% of all influenza cases are due to the type B strain.
"The utility of zanamivir against influenza B is important because other approved antiviral agents have no activity against this type of influenza virus," said Albert Osterhaus, DVM, PhD, chairman of the virology department at Erasmus Medical Centre, Rotterdam. "Physicians don't typically perform viral typing tests before treating patients, so having a drug that works equally well against influenza A and B should instill greater confidence among prescribers in the reliability of antiviral treatment."
To determine the effectiveness of zanamivir against influenza B, researchers analyzed data from patients who participated in the five international studies conducted as part of the approval process for the drug. Patients with influenza A or B were randomized to receive either zanamivir or matched placebo within two days of symptom onset and were maintained on therapy for five days.
Of the 1,572 patients enrolled in these studies, a total of 220 patients (11%) were confirmed to have influenza B. Results indicate that symptom duration was reduced by 25% (six days in placebo group vs. 4½ days in the zanamivir treated group). Similar efficacy was observed in the treatment of influenza A (6½ days in the placebo group vs. five days in the zanamivir treated group).
Zanamivir is indicated for the treatment of uncomplicated acute illness due to influenza virus in adults, and adolescents 12 years and older who have been symptomatic for no longer than two days. Patients inhale zanamivir orally using a hand-held, breath-activated device called a Diskhaler.
The most common side effects occurred in 3% or less of patients, were at rates comparable to placebo and included sinusitis, diarrhea and nausea. Safety and efficacy in patients with asthma or other chronic lung or heart disease have not been established.
For more information:
- Hayden FG. Influenza neuraminidase inhibitors. Abstract 1107. Presented at the 39th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC). Sept. 26-29. San Francisco.
- Osterhaus ADM, Makela MJ, Webster A, Keene ON. The efficacy of inhaled zanamivir in the treatment of influenza B. #281. Presented at the 39th Annual Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC). Sept. 26-29. San Francisco.
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