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Tamiflu: A Targeted Approach for Treating Influenza

Brand Name: Tamiflu
Active Ingredient: oseltamivir phosphate
Indication: Treatment of influenza A and B
Company Name: Hoffmann-La Roche Inc. and Gilead Sciences, Inc.
Availability: Approved for marketing in the US in October 1999

Introduction

TamifluSome 40 million Americans develop the flu every year, putting about 300,000 in the hospital. Up to 40,000 people die from influenza or its complications annually. Moreover, hospitalization and deaths due to the flu are increased among the elderly and those with high-risk medical conditions. The economic costs of the flu are high as well: some $14.6 billion due to lost wages, decreased productivity, and physician visits.

Arriving just in time for this year’s flu season, Tamiflu (oseltamivir phosphate) is the first neuraminidase inhibitor available in pill form. It is indicated for the treatment of uncomplicated acute illness due to infection with influenza A and B (which includes all common strains of the virus) in adults who have been symptomatic for no more than two days. Unlike over-the-counter medications that treat only the symptoms of the flu, Tamiflu actually targets the influenza virus and stops it from replicating. The recommended oral dose is 75 mg twice daily for five days.

How It Works

The neuraminidase protein is one of two major surface structures on the influenza virus and is virtually the same from one common strain of influenza to the next. The influenza virus needs neuraminidase to replicate and spread to other cells. In vitro studies showed that Tamiflu works by binding to the neuraminidase site and inhibiting its action, thus preventing replication of the influenza virus and its ability to spread from cell to cell.

Tamiflu (oseltamivir phosphate): Clinical Study Results

Tamiflu: A Targeted Approach for Treating InfluenzaThe efficacy of Tamiflu was demonstrated in two phase III double-blinded placebo-controlled trials, one conducted in the US and one outside the US. Eligible patients had a fever of more than 100 degrees F and at least one respiratory symptom (cough, nasal symptoms, or sore throat) and at least one systemic symptom (myalgia, chills/sweats, malaise, fatigue, or headache), and influenza known to be circulating in the community. Of 849 influenza-infected patients, 95% had influenza A, 3% had influenza B, and 2% had an unknown type.

Tamiflu administration commenced within 40 hours of onset of symptoms. Subjects participating in the trials were required to assess their symptoms as none, mild, moderate, or severe. Time to improvement was defined as the interval between the initiation of treatment to the time when all symptoms could be described as none or mild. In both studies, influenza-infected patients who received 75 mg of Tamiflu twice daily for five days showed a 1.3 day reduction in time to improvement of symptoms when compared to patients receiving placebo. The results were similar among men and women and in the elderly.

Recent studies have demonstrated that Tamiflu may be able to prevent infection with influenza A and B. However, the drug is not approved for this indication at this time.

What the Patient Should Know

Nausea and vomiting were the most common adverse events reported in patients taking Tamiflu, and to a lesser extent, bronchitis, insomnia, and vertigo. These events were generally mild and transient. Patients are advised to begin Tamiflu treatment as soon as possible after the initial appearance of symptoms. Finally, Tamiflu is not a substitute for a flu shot. Patients should continue receiving an annual flu shot according to immunization guidelines.

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