General Information

The influenza virus is an exceptionally contagious viral infection that attacks the entire body, causing symptoms ranging from muscle aches and sore throat to fever and respiratory complications. An effective treatment is in demand, especially since influenza outbreaks kill 20,000 to 40,000 people in the U.S. annually.

Tamiflu is a neuraminidase inhibitor designed to attack the neuraminidase protein, one of the two major surface structures of the influenza virus. Since the protein receptor sites are nearly identical in all common strains of influenza, Tamiflu, the first neuraminidase inhibitor in pill form, is effective in preventing the spread of both the A and B strains of the virus within the body. This is contrary to earlier drugs which were effective in treating only one strain. Furthermore, this pill (along with its counterpart, Relenza [zanamivir], which has a similar effect but is inhaled) also has the advantage of affecting flu virus later in its life cycle, so is less likely to cause genetic mutations that lead to drug resistance. Tamiflu is indicated for the treatment of uncomplicated acute illness due to influenza infection in adults who have been symptomatic for no more than two days.

Mechanism of Action

Oseltamivir is an ethyl ester prodrug requiring ester hydrolysis for conversion to the active form, oseltamivir carboxylate. The proposed mechanism of action of oseltamivir is via inhibition of influenza virus neuraminidase with the possibility of alteration of virus particle aggregation and release (FDA label).

Side Effects

The most common side effects experienced by participants in the study were nausea and vomiting. These symptoms were mostly mild to moderate and generally occurred within the first two days of administration of the drug.

Other less frequent side effects included

·         Diarrhea

·         Bronchitis

·         Abdominal pain

·         Dizziness

·         Headache

·         Cough

·         Insomnia

·         Vertigo

·         Fatigue

Do not take Tamiflu if you are allergic to oseltamivir phosphate or any other ingredients of Tamiflu. Before starting treatment, make sure your doctor knows about any other medications you may be taking or if you have any form of kidney disease. The effects of Tamiflu on children (under the age of 18) and on human pregnancies have not yet been determined.

Dosing/Administration

The recommended dose is 75 mg twice daily for five days. Although studies indicate that Tamiflu may contribute to prevention of the virus, researchers advise that the drug is not a substitute for the influenza vaccine but rather a supplement to it. However, for people who cannot be vaccinated for medical reasons, such as allergies, Tamiflu may be a viable alternative.

Clinical Trial Results

A total of 1,355 patients participated in two phase 3, placebo-controlled, double-blind trials, one inside the U.S. and one outside of the U.S. Patients qualified for the study if they had a fever of over 100F accompanied by at least one respiratory symptom and at least one systemic symptom, and if their community was currently affected by a circulating influenza virus. Patients' ages ranged from 18 to 65. Most were affected by type A influenza, although some patients had type B, while others had an unknown strain of the virus. Five-day treatment was started within 40 hours of the onset of symptoms. At the onset of treatment, participants were asked to self-assess their symptoms as either "none," "mild," "moderate" or "severe." Time to improvement was calculated from the beginning of treatment to the point at which a patient described his or her symptoms as "none" or "mild."

Results showed that median time to improvement was 1.3 days (30 percent) fewer for participants taking Tamiflu than those who were given a placebo. There were no significant differences between the effects on men and women, neither did increased dosage significantly affect results.

Additional Information

For additional information about the influenza virus and prevention methods, visit the Centers for Disease Control Influenza home page: cdc.gov/ncidod/diseases/flu/fluvirus.htm