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S’pore woman developed mutated bug within 48 hours after Tamiflu treatment
SINGAPORE scientists have discovered that the Influenza A (H1N1) virus can mutate into a drug-resistant form virtually overnight.
This new research contrasts with previous findings, which showed resistance from four to 14 days after oseltamivir, better known as Tamiflu, is used.
The report, published online yesterday and in next month’s issue of Emerging Infectious Diseases Journal, cited a case in May last year of a 28-year-old woman here who developed the mutated bug within 48 hours of being treated with Tamiflu – the fastest on record internationally.
She had developed a sore throat, cough, myalgia (muscle ache), redness in the right eye and a mild fever on the day she returned from Hawaii.
A mutation associated with the drug-resistant virus was detected in a virus isolated from the patient after she was given Tamiflu, but not when she was first infected.
This, the team found, was similar to the speed at which the Influenza A (H3N2) virus, which caused the Hong Kong flu, developed resistance to adamantanes, one of the older anti-viral drugs.
Dr Timothy Barkham, one of the authors of the paper, told The Straits Times that the finding was “an exceptional case”.
The patient and 11 of her close contacts were given Tamiflu. The 11 remained well.
“But then we didn’t test everyone at all times.
We would probably have recorded more if we had,” said the senior consultant from the clinical microbiology
department of laboratory medicine at Tan Tock Seng Hospital.
He worked with Professor Masafumi Inoue from the Agency for Science, Technology and Research and other clinician scientists on the research.
“This is one good example of solid teamwork by clinicians and researchers,” Prof Inoue said.
While alarm bells went off when the researchers discovered how quickly the virus can mutate to resist
Tamiflu, Dr Barkham said “over 99 per cent of the virus is still susceptible to the drug”.
He added that doctors should consider resistance when patients seriously ill with flu fail to respond
to treatment for H1N1.
Noting that anti-virals are likely to be most effective in cases of severe flu, he said: “We should not give patients anti-viral drugs unless it is really necessary, to preserve them for patients who really need them.”
Previously, there had been Tamiflu-resistant strains of the H1N1 virus reported, but these cases had been in immuno-compromised patients and had taken 11 to 23 days to develop.
More recently, drug-resistant strains took between four and 14 days of treatment with Tamiflu to develop.
When the H1N1 pandemic broke out in March last year, doctors feared it could become worse.
The H1N1 pandemic is over and the virus is now classified as a type of seasonal influenza.
Tamiflu is made and distributed by Roche, while another vaccine, Relenza, known generically as zanamivir,
is made by GlaxoSmithKline.
A Health Ministry spokesman said its current stockpile of Tamiflu can treat up to 1.39 million adults and 300,000 children, and its Relenza stockpile is enough to treat about 750,000 people.
“Our stock of H1N1 vaccine currently stands at 780,000 doses,” he added.
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