Drugmakers’ traditional model is under threat from looming loss of exclusivity on some of the industry’s biggest sellers.

Pfizer is buying rival drug maker Wyeth in a -billion deal that will increase its revenue by 50 percent and solidify its No 1 rank in the industry.

Pfizer Inc was close to a -billion purchase of US rival Wyeth in a move to diversify its revenue base, sources familiar with the situation said.