Efficacy Study of Early Versus Late Oseltamivir Administration for Treating and Preventing Influenza

This study is a randomized, blinded, placebo-controlled clinical efficacy trial to assess the duration and severity of influenza symptoms, and duration of viral shedding, in influenza patients receiving oseltamivir early and late relative to placebo.

There are two main hypotheses in this study:

1. The duration of influenza symptoms, mean severity score, and duration of viral shedding are reduced in patients who initiate oseltamivir treatment late (48 to 119 hours) compared to those receiving no antiviral therapy.
2. Prior influenza vaccination (same season) reduces the duration of influenza symptoms and mean symptom severity in patients receiving oseltamivir after adjusting for age and timing of antiviral therapy (early versus late).

There are two secondary hypotheses:

1. The duration of influenza symptoms, mean severity score, and duration of viral shedding are reduced in patients with influenza who initiate oseltamivir treatment early (\< 48 hours) versus late (48 to 119 hours).
2. The incidence of secondary complications is lower in patients initiating oseltamivir therapy late relative to those receiving no antiviral therapy.

In the past decade influenza has become increasingly recognized as a serious disease and pandemic threat. Elderly persons, young children, and individuals with chronic medical conditions have the greatest risk for complications or death from influenza infection. Neuraminidase inhibitors are currently licensed for the treatment and prevention of influenza if started early in the course of illness, but little is known regarding the effects of oseltamivir (one neuraminidase inhibitor) on illness severity when initiated later in the course of illness. Greater knowledge of the treatment effects is urgently needed for optimal management of seasonal influenza, and to maximize use of a limited stockpile of antiviral drugs in the event of an influenza pandemic.

Eligibility Criteria:
Inclusion criteria:

1. Outpatient or inpatient encounter for acute respiratory illness less than 5 days (120 hours) duration.
2. Acute respiratory illness with feverishness OR cough.
3. Access to the internet or telephone at home. This is required because symptom severity reports will be submitted twice daily using either a secure web-based form or automated telephone entry. All phones in the Marshfield area have touchtone service, allowing automated data entry.

Exclusion criteria:

1. Institutional resident (including assisted living or skilled nursing facility).
2. Self-reported chronic liver or kidney disease. These conditions are listed as precautions in the oseltamivir manufacturer package insert (www.rocheusa.com/products/tamiflu/pi.pdf).
3. Pregnancy or breast-feeding. Oseltamivir is classified as pregnancy category C, and it is excreted in breast milk. The package insert states that the drug should be used only if the potential benefit justifies the potential risk to the fetus or breast-fed infant.
4. Prior hypersensitivity reaction to oseltamivir.
5. Dementia, impaired communication, or other reason for inability to provide informed consent.
6. Immunocompromised status, including HIV infection, neutropenia, systemic corticosteroid use, or use of other immunosuppressive drugs in the past 30 days. The manufacturer states that the efficacy of oseltamivir has not been established in immunocompromised patients.
7. Patient received 1 or more doses of influenza antiviral agents (oseltamivir, zanamivir, amantadine, rimantadine) or a prescription for one of these drugs prior to randomization.