Roche Holding AG said on Thursday it had halted deliveries of Tamiflu to the United States and Canada until the start of the flu season. Media coverage of the spread of the deadly H5N1 strain of bird flu had driven sales higher, the company said.
"This resulted in increased demand for Tamiflu in part from individuals who are doing private stockpiling and at the moment there is no influenza circulating and the threat of a pandemic has not [materialised]," a spokeswoman said.
"Our priority is to ensure that Tamiflu is available for seasonal use and to fulfil government orders," she added.
Healthcare information collector Verispan said more than 67,000 US Tamiflu prescriptions were dispensed for the week ending 21 October - quadruple the demand from the same week last year.
Tamiflu is considered the first line of defence against the H5N1 avian flu virus that some fear could spark a catastrophic pandemic if it mutates to allow human-to-human transmission.
The drug can reduce the severity of influenza and may slow its spread.
Governments are scrambling to buy it, but production is limited. Under pressure from generic drug companies, developing nations and the United States, Roche agreed this month to discuss granting licences to others to make versions of Tamiflu.
Mass culling of birds is under way
to prevent a pandemic
Cao Minh Quang, head of Vietnam's Pharmaceutical Control Department, said it had asked Roche to franchise Tamiflu production to Vietnam, where bird flu has killed 41 people.
"But in the situation of a pandemic, we will start the production without permission," Quang said.
Some experts have predicted that, should H5N1 mutate to become a human disease, an epidemic could be contained with the quick use of drugs such as Tamiflu and widespread quarantines.
Health officials have urged quick notification of suspected cases, and France and China both reported potential H5N1 human infections earlier this week.
But on Thursday France said tests on one of three tourists suspected of catching H5N1 in a Thai bird park showed he was not infected.
And China said a girl who died also tested negative.
H5N1 avian flu has forced the destruction of more than 140 million birds in Asia and the eastern parts of Europe and officials say it is on a steady march across the world.
So far it has affected only 121 people and killed 62 in four Asian nations - Cambodia, Vietnam, Thailand and Indonesia. But much of the Tamiflu buying is due to fears that governments are doing little to stop it.