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R/£ Tamiflu cure could be making H1N1 stronger
August 27, 2009 Edition 1
Los Angeles: Indiscriminate use of antiviral medications to prevent and treat influenza could ease the way for drug-resistant strains of the novel H1N1 virus, or so-called swine flu, to emerge, public health officials warn - making the fight against a pandemic that much harder.
Already, a handful of cases of Tamiflu-resistant H1N1 have been reported this summer, and there is no shortage of examples of misuse of the antiviral medications, experts say.
People often fail to complete a full course of the drug, according to a recent British report - a scenario that encourages resistance.
Stockpiling is rife, and some US summer camps gave Tamiflu prophylactically to healthy kids and staff. Experts anticipate more problems as children return to school and normal flu season draws nearer.
"Influenza viruses mutate frequently, and any viral resistance could be acquired easily," said Dr Anne Schuchat, director of the National Centre on Immunisation and Respiratory Disease at the Centres for Disease Control and Prevention in Atlanta.
"It won't surprise us if we see resistance emerge as a bigger problem in the fall or in the years ahead."
Prescribed in pill form, Tamiflu (oseltamivir) works by preventing the flu virus from leaving infected cells and spreading to new ones.
Because a vaccine against pandemic H1N1 influenza will not be widely available for several months, Tamiflu and to a lesser extent Relenza (zanamivir), an antiviral that acts similarly, are key medical tools for fighting the pandemic in the meantime.
Last week, the World Health Organisation advised doctors that even those sickened with the H1N1 virus do not need to be given Tamiflu or Relenza if they are mildly or moderately sick and are not in a high-risk group (such as children younger than five, pregnant women and those with an underlying health condition).
Anxiety over indiscriminate use is growing, and taking the medications cavalierly is not without consequence.
British health authorities reported on August 2 that cases of side-effects from Tamiflu had doubled in the prior week, coinciding with the July 24 launch of a programme in England to provide antivirals to anyone with H1N1 influenza who requested it over the phone or online.
In the first three days of the programme, 150 000 packets of Tamiflu were dispensed and 293 cases of side-effects were reported. Tamiflu can cause vomiting, diarrhoea and mild neuropsychiatric effects.
A study published in late July found poor adherence among children in London who took Tamiflu for prevention of H1N1 in the spring.
Less than half the grade-school-age children and 76 percent of the 13- and 14-year-old students completed a full course of medication.
More than half the children reported side-effects, such as nausea, stomach cramps and trouble sleeping. Almost one in five reported a neuropsychiatric side effect, such as poor concentration, confusion or bad dreams, even though the US Food and Drug Administration says neuropsychiatric side-effects are rare. Antiviral drugs can be underused as well as overused, said Dr Robert Schechter, acting chief of the immunisation branch of the California Department of Public Health.
Some Californians who died from novel H1N1 influenza did not receive antivirals.
A handful of resistant H1N1 cases have been reported among people who took Tamiflu preventively: three in Japan and one each in Canada, Hong Kong and Denmark.
Those cases are not surprising, nor of great concern to health authorities, said Dr Tim Uyeki, a medical epidemiologist with the CDC.
They are cropping up sporadically and don't seem to be spreading from person to person.
"The most important question for public health is not whether sporadic cases occur but whether there is ongoing transmission of oseltamivir-resistant strains," Uyeki said.
A study published in March about the spread of the H5N1 avian flu, which has been circulating in bird flocks in recent years and has killed 262 people, showed the virus rapidly developed resistance to a different class of antiviral drugs, adamantanes.
"With bird flu, we found some resistance started in China and spread throughout the world in a few years," said study author Daniel Janies, an evolutionary biologist at Ohio State University.
"Overuse contributes to resistance. Basic natural selection predicts it.
"We can demonstrate why you should not use these drugs unless you have to." - Los Angeles Times
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