In response to requests from the US Centers for Disease Control and Prevention, US FDA authorized emergency use of Tamiflu and Relenza to treat Swine Flu.
The flu (influenza) is an illness caused by different influenza viruses. It spreads rapidly in seasonal epidemics. Influenza attacks mainly the upper respiratory tract - the nose, pharynx, and rarely the lungs. It is characterized by sudden onset of high fever, body aches, chills, fatigue, headache, severe malaise, cough, and runny nose.
The first flu virus was identified in the 1930s. The dreadful pandemic (called the Spanish flu) occurred in 1918 when the virus caused more than 40 million deaths in the world, with a mortality rate of about 2-20%.
There are three types of influenza virus: A, B, and C. Types A and B are the most severe. The viruses change constantly and different strains circulate around the world every year. Type C causes either a very mild illness, or has no symptoms at all. It does not cause epidemics and does not have the severe public health impact that influenza types A and B do.
Antivirals for influenza are used for prevention or treatment of flu viruses. They work by decreasing the ability of flu viruses to reproduce.
For flu treatment, antivirals should be started within 2 days after illness onset. When used correctly, they can reduce the severity of symptoms and shorten the duration of flu attack by 1 or 2 days. They may also prevent flu complications.
When used for flu prevention, they are about 70-90% effective against susceptible viruses.
Flu antivirals include:
The Advisory Committee on Immunization Practices (ACIP) recommends to use only zanamivir and oseltamivir. Amantadine and rimantidine should not be used for influenza until the susceptibility among circulating influenza A to these antivirals has been reestablished.
Amantadine and rimantadine, known as adamantanes or M2 inhibitors, have been used as first-choice antivirals against influenza A viruses for many years. However, high rates of resistance among influenza A viruses deplete the adamantanes usefulness.
Adamantanes inhibit the activity of the influenza virus M2 protein, which forms a channel in the virus membrane. As a result, the virus cannot make copies of itself after it enters a cell.
Amantadine and rimantadine have comparable effectiveness in treating or prevention influenza A. However, rimantadine has lower potential for causing central nervous system side effects than amantadine.
A second class of antivirals for influenza is the neuraminidase inhibitors, which includes oseltamivir and zanamivir. They work on a broader spectrum of influenza strains and have activity against both influenza A and B viruses, and highly pathogenic H5N1 isolates.
Neuraminidase is an enzyme that helps release new virus particles from infected cells. Neuraminidase inhibitors block the action of neuraminidase thereby preventing the release of new copies from infected cells. By preventing the spread of virus from cell to cell, the symptoms and duration of flu are reduced.
Flu antivirals are most effective when given within 48 hours of the onset of illness. They can decrease the duration of the disease by 1 to 2 days if used within this early time period. They are usually given for a period of about 5-7 days.
Zanamivir (Relenza) is an inhaled powder that comes with a device called Diskhaler. It should not be used in people with chronic lung disease.
Last updated: April, 2011