EFFECTIVENESS AND SAFETY

The currently approved treatment for seasonal influenza with neuraminidase inhibitors requires a 5-day regimen1 (one 75 mg capsule two times per day of oseltamivir, or two inhalations two times per day of zanamivir), while prophylaxis for exposure to seasonal influenza virus requires a 10-day regimen (one capsule per day or two inhalations per day). Randomized trials have demonstrated efficacy when neuraminidase inhibitors, in particular oseltamivir, were used for prophylaxis after exposure in both family and institutional settings and when used for 6 weeks as seasonal prophylaxis in nursing homes (Moscona, 2005; Hayden and Pavia, 2006). Data from a study of hospitalized adults demonstrated a strong association between oseltamivir use and decreased mortality (adjusted odds ratio 0.21) (McGeer et al., 2007). The two major gaps in the research on neuraminidase inhibitor effectiveness include lack of high-quality data in high-risk persons and lack of adequate data for H5N1.

Although neuraminidase inhibitors have not been studied or approved for prolonged use beyond 6 weeks, protecting vulnerable health care and other workers during a pandemic may require prophylaxis over several weeks or longer. Pandemic duration likely will depend on the success of non-pharmaceutical interventions in “flattening” (CDC, 2007c) the pandemic curve. This refers to decreasing and extending the plotted course of a pandemic, which in the absence of effective interventions the first wave of a pandemic is expected to have an earlier, more severe peak in the number of cases per week. Modeling and data from the 1918 pandemic suggest that effective non-pharmaceutical interventions would delay and decrease the height of the peak, but result in a longer duration of the pandemic wave (IOM, 2006). However, models have limitations, and the vastly different socio-cultural setting of historic data must be acknowledged.

Neuraminidase inhibitors are effective in treating influenza and are currently used to prevent some cases during seasonal influenza outbreaks. Randomized trials, conducted primarily among relatively healthy children and adults, have demonstrated decreased duration of symptoms, disability, antibiotic use, and decreased time to return to normal function after treatment (Moscona, 2005). However, treatment is most effective when given as early as possible after symptoms develop, and its effectiveness diminishes markedly after 48 hours. Data are limited on the efficacy in high-risk populations. The available data suggest decreased hospitalization and mortality rates with treatment; however these are derived

1

Oseltamivir adult dose: 75 mg bid for 5 days for treatment, 75 mg qd for 10 days for prophylaxis (Roche Pharmaceuticals, 2008); oseltamivir pediatric dose (ages 1–12 years): ≤33 lbs, 30 mg/bid/5 days; >33 lbs to 51 lbs, 45 mg/bid/5 days; >51 lbs to 88 lbs, 60 mg/bid/5 days; >88 lbs, 75 mg/bid/5 days (add: same dose qd/10 days for prophylaxis).



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