Roche is increasing production of its Tamiflu antiviral medicine in response to fresh orders for the drug sparked by fears of a flu pandemic spreading from Mexico.

The Swiss pharmaceutical company said it would be able to produce 36m packs a month by the end of this year as governments add to stockpiles and begin using it for treatment, raising the prospect that it will again become a $1bn-a-year blockbuster drug after a recent drop in demand.

It added that it was donating nearly 5.7m extra treatments for distribution by the World Health Organisation to low-income countries, after a previous 5m gift has been dispatched in recent days and pressure grows for alternative supplies from low-cost generic rivals.

Governments round the world have stockpiled 220m treatments to date, swelling sales since the start of 2003 to SFr7.6bn ($6.9bn), largely on the basis of preparation for a pandemic virus that has yet to appear. With reserves built and few countries outside Japan using the drug on any large scale to treat seasonal flu, sales had dropped off.

David Reddy, head of Roche’s global pandemic preparedness task force, confirmed that the company was in talks that could lead to further reductions of its pandemic price of €12 ($16.30) a treatment for poorer countries. It charges €15 to richer countries.

He said: “Governments have been ordering additional supplies over the last couple of weeks and we are getting inquiries from less-developed countries.

“But we want to understand the level of demand. Most orders are coming from developed and middle income countries.”

The company has licensed an Indian, South African and two Chinese generic companies to produce and sell Tamiflu at whatever price they choose but rivals, including Cipla of India, are pushing to override Roche’s patent. No generic company has yet received approval from the WHO to produce the drug.

The WHO said on Tuesday that there had been at least 61 deaths and 5,251 confirmed H1N1 infections in 30 countries so far.

It has called for pharmaceutical companies to ease access to drugs and vaccines for the poor but cautioned that most patients did not require treatment with Tamiflu to recover.