A multitude of factors are coming together to bring a big burst in biotech M&A.

The high-profile bidding war between Pfizer

and Novo Nordisk over Metsera and its leading weight loss drug candidate shows just how competitive some pockets of the sector have become, as Big Pharma frantically works to fill the looming revenue hole.

Some of the best-selling drugs in the world are facing a loss of exclusivity in key jurisdictions in what the sector calls “the patent cliff.” By 2032, losses of exclusivity for best-selling brands are worth at least $173.9 billion in annual sales, according to CNBC calculations. Estimates vary on the total amount of revenue at risk when factoring in smaller brands, with some analysts putting the number between $200 billion and $350 billion.

That poses a real threat to their makers’ top lines — unless they manage to replenish their pipelines with new, revenue-bearing innovations.