Treating influenza by medication – Zanamivir

Findings by SBU Alert

This is a translation of version 1, published on January 12, 2001. The information and references added on May 4, 2004 is not incorporated in this English translation.

Method

Zanamivir (Relenza) is an antiviral drug indicated for treatment of influenza. The drug was approved in Sweden in February 1999. Zanamivir is a powder for administration to the respiratory tract by oral inhalation via a Diskhaler. For treatment to be effective, it must be initiated within 48 hours of the onset of influenza symptoms. An examination by a physician is required prior to treatment to establish the diagnosis, to exclude patients with contraindications, and to provide specific instructions on the use of the Diskhaler.

Patient benefits, complications, and side effects

The efficacy of zanamivir has been evaluated in three randomized, controlled trials, predominantly involving previously healthy adults. A pooled analysis of these three studies showed that zanamivir reduced the duration of symptoms of influenza by 1,0 days (median value) in the entire population. In rare cases, particularly in patients with underlying chronic obstructive pulmonary disease, serious adverse reactions such as bronchospasm and decline in lung function have been reported in close temporal association with the use of zanamivir. During the influenza season, the waiting rooms of community health centres and hospitals can be crowded with patients with acute influenza-like symptoms, which may increase the risk for transmission of the disease.

Cost effectiveness

A model analysis from Great Britain estimated that the health gains from treating patients with zanamivir, converted to cost per quality-adjusted life-year gained, yields a cost of approximately 500 000 SEK, corresponding to approximately 1 400 SEK per day.

Scientific evidence

There is good* scientific evidence that zanamivir can alleviate symptoms in previously healthy adults. Satisfactory documentation is lacking as regards treatment effects in patients at increased risk for complications of influenza, ie, the elderly (>65 years) patients with cardiovascular and/or pulmonary disease, metabolic diseases (e.g. diabetes), and patients with an impaired immune defense.

Given the limited benefits of zanamivir in previously healthy adults with influenza, treatment should be restricted to individuals belonging to the medical risk groups at risk for contracting serious secondary complications. In using zanamivir, one should balance the severity of the disease against the relatively high cost per health benefit, and also consider that the effects in the medical risk groups have not been sufficiently studied. Furthermore, the cost effectiveness and consequences on healthcare organizations need to be studied further.

*This assessment by SBU Alert uses a 4-point scale to grade the quality and evidence of the scientific documentation. The grades indicate: (1) good, (2) moderate, (3) poor, or (4) no scientific evidence on the subject.

This summary is based on a report prepared at SBU in collaboration with Agneta Björck Linné, Dr Med Sci, Malmö University Hospital, Assoc. Prof. Hans Liedholm, Malmö University Hospital and Assoc. Prof. Ingrid Uhnoo, Medical Products Agency.

The complete report is available in Swedish only.

Alert is a joint effort by the Swedish Council on Technology Assessment in Health Care (SBU), the Medical Products Agency, the National Board of Health and Welfare, and the Federation of Swedish County Councils.

References

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3. Hayden FG, Osterhaus A, Treanor JJ, Fleming DM, Aoki FY, Nicholson KG, Bohnen AM, Hirst HM, Keene O, Wightman K. Efficacy and safety of the neuraminidase inhibitor zanamivir in the treatment of influenzavirus infections. N Engl J Med 1997;337:874-80.
4. MIST. Randomised trial of efficacy and safety of inhaled zanamivir in treatment of influenza A and B virus infections. The MIST (Management of influenza in the Southern Hemisphere trialist study group). Lancet 1998;352:1877-81.
5. Monto AS, Fleming DM, Henry D,de Grot R, Makela M, Klein T, Elliott M, Keene ON, Man CY. Efficacy and safety of the neuraminidas inhibitor zanamivirin the treatment of influenza A and B virus infections. J Infect Dis 1999;180: 254-61.
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7. Monto AS, Webster A, Keene O. Randomised placebocontrolled studies of inhaled zanamivir in the treatment of influenza A and B: pooled analysis. J Antimicrobial Chemotherapy 1999;44:23-29
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9. Mäkelä MJ, Pauksen K, Rostila T, Fleming DM, Man CY, Keene ON, Webster A. Clinical efficacy and safety of the orally inhaled nuraminidase inhibitor zanamivir int the treatment of influenza: a randomised double-blind, placebo-controlled Eurpean study. Journal of Infection 2000;40: 42-4.
10. Nicol KL, Margolis KL, Wuorenma J, Von Sternberg T. The efficacy and cost effectiveness of vaccination against influenza among elderly persons living in the community. N Eng J Med 1994;331:778-84.
11. Produktmonografi för Zanamivir. Information från Läkemedelsverket 1999;4:27-32