Oseltamivir (Tamiflu) unsafe in infants under 1 year old

Reason for posting: Influenza is a common and potentially serious infection in children. Neuraminidase inhibitors are sometimes used to treat and prevent the disease in some children. However, the US Food and Drug Administration (FDA) recently warned that studies involving juvenile rats showed potential toxicity of oseltamivir for human infants less than a year old (www.fda.gov/medwatch/SAFETY/2003/safety03.htm#tamiflu).

The drug: Oseltamivir (Tamiflu) inhibits the influenza neuraminidase enzyme, thus preventing the release and dispersion of budding viruses. In Canada the drug can be used to treat influenza in children older than 1 year with symptoms of less than 2 days' duration and to prevent the disease in children over 13 years old.

The unpublished trial described by the FDA involved 7-day-old rats being fed a single dose of 1000 mg/kg of oseltamivir — about 250 times the dose recommended for children. The treatment was toxic, often killing the animals, and brain levels of the drug were 1500 times those of adult animals exposed to the same dose. It is hypothesized that an immature blood–brain barrier may cause the toxicity.

What to do: Oseltamivir should not be given to children less than a year old. Basic infection control precautions such as keeping the child away from sick people, frequent handwashing and flu shots (for children over 6 months old and caregivers) may be the best way to prevent the disease. The relative safety profile of other antiviral agents (amantadine, zanamivir) in the very young pediatric population is unclear. — Eric Wooltorton, CMAJ