November 23, 2009
As public health officials urge more rapid use of antivirals for H1N1, some experts worry the drugs could become over-prescribed for what is a relatively mild illness in most people.
More than one million antiviral doses have been drawn from the federal stockpile in recent months, and the number of prescriptions filled by Canadian retail drugstores for Tamiflu and Relenza, the frontline drugs being used in the pandemic, nearly doubled between September and October.
As of Oct. 30, 151,688 prescriptions had been dispensed by retail pharmacists nationwide so far this year -- an increase of 73,291 prescriptions over September, according to prescription-drug-tracking firm IMS Health Canada.
Nationally, the number of visits to doctors for flu-like symptoms are at levels not seen in 12 years.
The World Health Organization is recommending that people in at-risk groups, including pregnant women, children under two and those with underlying conditions such as asthma, be treated with antivirals as soon as possible when they have flu symptoms, and that people without risk factors should also be treated if their symptoms worsen or persist.
WHO says healthy people experiencing mild illness don't need antivirals. But the WHO warns the virus can cause severe pneumonia even in healthy young people.
"The window of opportunity is very narrow to reverse the progression of the disease," Dr. Nikki Shindo, a medical officer in WHO's Global Influenza Programme, said in a recent briefing.
"The medicine needs to be administered before the virus destroys the lungs." WHO is urging doctors not to wait for lab-confirmation before deciding to treat. Tamiflu, or oseltamivir, needs to be given within the first 48 hours of infection to be optimally effective.
"It's a bit of catch-22, when the best impact of the oseltamivir is if you give it early. And yet we're not suggesting that the huge majority of people get oseltamivir," said Dr. Brian Ward, an infectious-disease physician and associate director of The Research Institute at McGill University Health Centre.
"Most of the people who have true influenza should not be prescribed oseltamivir," Ward said.
The drugs can cause nausea and vomiting, and widespread use could lead to H1N1 developing resistance to the only effective antivirals available.
"Really, the cutoff is clinical symptoms out of proportion for what you would expect for routine influenza," Ward said.
He had H1N1 in the summer, "and I very specifically did not take oseltamivir. I didn't want to spread a resistant bug to my children and family. And I had flu. I didn't have unexpected symptoms.
"We should be reserving the oseltamivir for people who are presenting with unusual symptoms." For most people, that would be unexpectedly or surprisingly severe respiratory distress, he said.
"In a very young child, it would be rapid onset of very high fever with respiratory distress . . . or an older child who does OK for a day or two -- so muscle aches, headaches, a little bit of cough -- who suddenly starts having difficulty breathing." In addition, for children with asthma, the threshold for starting Tamiflu "is way, way lower" than it would be for an otherwise healthy child, Ward said.
According to Health Canada, Tamiflu has been shown to reduce the symptoms of illness by, on average, 1.3 days, or 30 hours. An average course of flu lasts approximately five to seven days.
"For the normal flu, they generally cut between a half a day and a day off of the length of symptoms," said Dr. Joel Lexchin, a professor in York University's School of Health Policy and Management.
"If we prescribe them for people with relatively mild flu, and the virus develops resistance, then they wouldn't be of very much use for people with severe cases of H1N1."
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