Influenza can cause serious complications in young children, including pneumonia and encephalitis (brain inflammation), and even death.  Babies younger than one year of age are 6-9 times more likely to die from influenza than older children are, although the rate of death is still very small (less than one death from influenza for every 100,000 children in the U.S.)

The drug we are studying is oseltamivir, which is also called Tamiflu.  Tamiflu is approved for treatment of children one year of age and older and who have had influenza symptoms for less than 2 days, and has recently received FDA approval for influenza prophylaxis (prevention) down to one year of age as well.  The use of Tamiflu in children whose influenza symptoms started more than 2 days before treatment begins has not been approved by the FDA. Of the four drugs licensed for the treatment of influenza, Tamiflu is the only one that comes in a liquid form and is currently the only one recommended by the U.S. Centers for Disease Control and Prevention for the treatment of young children with the types of influenza found in the United States.

Although the FDA has agreed that Tamiflu is safe to be given to children between 12 and 23 months and that it treats influenza well, there are few studies that describe the levels of Tamiflu in the blood of 1-2 year old children.

The purpose of this study is to measure the amount of Tamiflu in the blood that would be effective to kill the influenza virus, and to find the dose of Tamiflu that is safe and well tolerated in children under 2 years of age.