Canadian infants under one year old who are sick with the flu may receive the antiviral drug Tamiflu, Health Minister Leona Aglukkaq announced Thursday under new swine flu pandemic guidelines.

The Public Health Agency of Canada prepared the interim guidance to help doctors treating infants with influenza-like illness during the H1N1 pandemic.

"The public health emergency created by the pandemic, and this group's increased vulnerability from influenza, created the urgent circumstances that deemed this necessary," Aglukkaq said.

"Although there are limited data supporting the use of Tamiflu in children under one, there now exists an urgent need for recommendations to treat this population, given this group's increased risk for morbidity and mortality from influenza," the agency said on its website.

Regulators in the United States and Britain have made similar changes, Dr. David Butler-Jones, Canada's chief medical officer of health, told a teleconference with reporters.

Doctors sought guidance

The change reflected the need to address practical concerns from physicians seeking official guidance from the minister on treating infants, instead of prescribing Tamiflu — a brand name for the drug oseltamivir — off-label based on guesses, Butler-Jones said.

The decision to treat sick infants with Tamiflu seems "fairly simple," he said, given the real risk of deaths, severe disease and hospitalization from the H1N1 virus, compared with the theoretical risk posed by a drug with a good safety profile in adults and young children.

Parents or guardians should be informed that the drug is being prescribed under "exceptional use," the agency said.

The drug may be prescribed for suspected cases of swine flu with a positive rapid test result, for children with a fever without another clear cause and a history of contact with an infected person, or in children with fever who are having trouble breathing.

The guidelines include dosing information by weight and age.

Another antiviral drug, Relenza (zanamivir), is currently indicated for children seven years or older, the agency said.

Earlier this week, Canada recorded its first case of Tamiflu-resistant swine flu virus. The Quebec man had been given the drug to prevent infection.

He had mild symptoms and fully recovered, and did not appear to spread the resistant strain.

Also on Thursday, Butler-Jones announced 12 hospital intensive-care units in Manitoba, Ontario, Quebec and Alberta have expressed interest in participating in a study examining why the H1N1 virus seems to be striking some people harder than others.

Researchers will examine the role of risk factors for severe infection, such as age, weight, gender, underlying disease and immunization.

They will also try to determine how long those who are seriously ill remain infectious and what the best treatment practices are, such as mechanical ventilation.