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Australian Journal of Pharmacy : October 2006
ucation suspension. It has good oral bioavailability and is converted to the active metabolite via the liver.23 It has a half life of six-to-10 hours and is excreted primarily via the kidneys.23 Thus, doses must be reduced in patients with kidney impairment. Efficacy A study conducted in the United States in 374 patients with confirmed influenza showed that oseltamivir reduced the median duration of the illness by more than 30 per cent (from 4.3 days to 3.0 days) and the severity of illness by about 40 per cent.24 There was a reduction in fever and a resolution of symptoms as soon as 24 hours after initiation of treatment.24 Other studies have showed that both zanamivir and oseltamivir, when administered within 24–36 hours, decreased symptoms of the illness by one-to- two days.23 Treatment that started within 12 hours reduced the illness by three days.23 Thus, early recognition of the illness and immediate initiation of treatment with a neuraminidase inhibitor is important in reducing illness severity. Other studies have also shown that both zanamivir and oseltamivir are effective in preventing clinical influenza in healthy adults when used as prophylaxis for close contacts of patients with influenza.23 Overall, both oseltamivir and zanamivir were 70–90 per cent effective when used for prophylaxis either before or after exposure to influenza A viruses.23 Safety Adverse effects of oseltamivir and zanamivir are listed in Table One. Dosing While it is not clear whether the dose or the duration of dosing will be sufficient to cope with infection from a pandemic resulting from the H5N1 virus, Table Two lists current recommendations for dosing. 1. Horimoto T, Kawaoka Y. Influenza: Lessons from past pandemics, warnings from current incidents. Nature reviews microbiology 2005:3;591–600. 2. Lamb RA, Krug RM. In: Fields Virology. Fields BN, Knipe DN, Howley PM(eds). Ch 46, Lippincott-Raven, Philadephia 2001. 3. Fouchier RA. Characterization of a novel influenza A virus hemagglutinin subtype (H16) obtained from black headed gulls. J Virol 2005:79;2814–2822. 4. Webster RF, Bean WJ, Gorman OT, Chambers TM, Kawaoka Y. Evolution and ecology of influenza A viruses. Microbiol Rev 1992;56;152–179. 5. Johnson NP, Mueller J. Updating the accounts: global mortality of the 1918- 1920 ‘Spanish’ influenza pandemic Bull Hist Med 2002:76;105–115. 6. Kobasa D. Enhanced virulence of influenza A viruses with the hemagglutinin of the 1918 pandemic virus. Nature 2004:431;703–707. 7. Simonsen L. Pandemic versus epidemic influenza mortality: a pattern of changing age distribution. J Infect Dis 1998:178;53–60. 8. Reid AH, Tauberberger JK, Fanning TG. Evidence of an absence: the genetic origins of of the 1918 pandemic influenza virus. Nature Rev Microbiology 2004:2;909–914. AJPCPE CONTINUING PROFESSIONAL EDUCATION 9. Scoltissek C, Rohde W, Von Hoyningen V, Rott R. On the origin of the human influenza virus subtype H2N2 and H3N2. Virology 1978:87;13–20. 10. Nakajima K, Desselberger U, Palese P. Recent human influenza A (H1N1) viruses are closely related genetically to strains isolated in 1950. Nature 1978:274;334–339. 11. de Jong JC, Claas ECJ, Osterhaus ADME, Webster Rg, Lim WL. A pandemic warning. Nature 1997:389;554. 12. Subbarao K. Characterization of an avian influenza (H5N1) virus isolated from a child with a fatal respiratory illness. Science 1998:279;393–396. 13. Cauthen AN, Swayne DE, Schultz-Cherry S et al. Continued circulation in China of highly pathogenic avian influenza viruses encoding the hemagglutinin gene associated with the 1997 H5N1 outbreak in poultry and humans. J Virol 2000:74;6592–6599. 14. Sturm-Ramirez KM. Reemerging H5N1 viruses in Hong Kong in 2002 are highly pathogenic in ducks. J Virol 2004:78;4892–4901. 15. Beare AS, Webster RG. Replication of avian influenza viruses in humans. Arch Virol 1991:119;37–42. 16. Cinti S. Pandemic influenza:are we ready? Disaster Managmt & Response 2005;3(3):61–67. 17. Patriarca PA, Cox NJ. Influenza preparedness plan for the United States. J Infect Dis 1997;176(supp 1):S4–S7. 18. Australian Management plan for pandemic influenza. June 2005. Australian Government Department of Health and Ageing. 19. The writing committee of the World Health Organization (WHO) consultation on human influenza A/H5. Avian influenza A (H5N1) infection in humans. N Engl J Med 2005;353(13):1374–1385. 20. Bridges Cb, Kuehnert MJ, hall Cb. Transmission of influenza: implications for control in health care settings. Clin Infect Dis 2003;37:1094–1101. 21. Mounts AW, Kwong H, Izurieta HS et al. Case-control study of risk factors for avian influenza A (H5N1) disease, Hong Kong, 1997. J Infect Dis 2002;185:1005–1010. 22. World Helath Organization. WHO interim guidelines on clinical management of humans infected by influenza A(H5N1). Feb 20, 2004. Accessed at: www.who.int/csr/avian_influenza/guidelines/Guidelines_Clinical%20Managem ent_HSN_rev.pdf 23. Moscona A. Neuraminidase inhibitors for influenza. N Engl J Med 2005;353:1163–1173. 24. Treanor JJ, Hayden FG, Vrooman PS et al. Efficacy and safety of the oral neuraminidase inhibitor oseltamivir intreating acute influenza: a randomized controlled trial. JAMA 2000;283:1016–1024. ¦ *Margaret Robinson is Adjunct Professor School of Life Sciences, Queensland University of Technology, and a senior lecturer at the School of Pharmacy, University of Queensland. This abridged Drug Review is reproduced with the support of Gold Cross from the New Drug Brief, an information service provided for pharmacists by Gold Cross Products and Services on behalf of the Pharmacy Guild of Australia and reproduced in the AJPwith permission. For more information or to subscribe to the New Drug Brief, visit www.goldx.com.au/member/services.htm THE AUSTRALIAN JOURNAL OF PHARMACY VOL.87 OCTOBER 2006 ? 87