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.