Tests on the latest suspected human cases of the disease produced negative results on Thursday, but fear remained high that bird flu was spreading around the world among wild birds and poultry and threatened to produce a human pandemic.
Roche Holding AG said it had halted deliveries of Tamiflu to pharmacists in 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 has 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.
British-based GlaxoSmithKline Plc, Europe's biggest drug maker, said on Thursday it was building capacity and converting more factories to make a pandemic flu vaccine, as it develops a prototype shot to counter the H5N1 bird flu virus.
It also plans to increase output of the anti-flu drug Relenza and is offering free licences to partners able to produce the inhaled treatment. Relenza, like Roche's Tamiflu, is not a cure but reduces the severity of influenza.
Roche is the only manufacturer of Tamiflu, considered the first line of defence against the H5N1 avian flu virus that some fear could spark an outbreak among humans if it mutates to allow human-to-human transmission. The drug can reduce the severity of influenza and may slow the spread of a pandemic.
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.