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First there were rumors surrounding AstraZeneca, then Botox-maker Allergan was caught in a takeover storm and on Tuesday GlaxoSmithKline (GSK) and Novartis announced a $16 billion commercial tie-up. The pharmaceutical industry has been swept up in a wave of mergers and acquisitions.

Industry observers have been waiting for a rush of deals for months, as cash-rich companies work to reshape themselves. And over Easter weekend, that activity sharply picked up pace.

Rumored tie-ups in the sector now include a whopping $100 billion bid for AstraZeneca by Pfizer, the biggest company in the sector, and a mooted $50 billion pitch for Botox maker Allergan by Valeant and activist investor Bill Ackman.

There are several factors driving companies to make deals at the moment: such as the sector's well-publicized difficulties with developing new products and pricing as well as a move to exploit a U.S. tax law.

One deal which is definitely going ahead is GSK and Novartis' trade-off of different areas of their businesses, announced Tuesday morning.

GSK will get most of its Swiss rival's vaccines business and its consumer healthcare, while Novartis will pay up to $16 billion for GSK's oncology business. In the meantime, Eli Lilly of the U.S. is to pay $5.4 billion for Novartis' animal health division.

This is an unusual set of moves, in a sector where traditionally huge companies have swallowed up their slightly smaller rivals.

Price pressures around the world are one of the key factors driving the wave of deal-making at the moment, Andrew Witty, chief executive of GlaxoSmithKline, told CNBC.

"This is about how industry players need to be positioned over the next decade. You need to look forward 10-20 years rather than two-three years," he said.

Yet this is not just about buying in a better pipeline for the future.

U.S. tax law is one of the key factors driving companies to make deals. If at least 20 percent of a U.S. company's shares are held overseas, it can re-domicile its tax base and make savings on its tax bill. Buying a foreign domiciled company can be a quick win for U.S. pharma groups, which mostly have a solidly American shareholder base, to bring in more overseas shareholders.