Pfizer has gone public about its interest in buying AstraZeneca and revealed that management at the latter has twice declined to get into any serious discussions about a possible merger.

The US giant notes that it first made an approach in January but "after limited high-level discussions, AstraZeneca declined to pursue negotiations". The cash-and-stock proposal was worth £46.61 per share, a 30% premium to AstraZeneca’s closing share price of £35.86 on January 3, valuing the deal at just under £59 billion.

Pfizer now reveals it came back on Saturday (April 26) "to develop a proposal that could be recommended by both companies to their shareholders". AstraZeneca again declined to engage and Pfizer is currently considering its options; a conference call will be held later today (1.30pm UK time).

The New York-headquartered behemoth says it is "confident a combination is capable of being consummated", adding that a combination of the two firms would establish a new UK-incorporated holding company. That would mean that AstraZeneca’s non-US profits would not be subject to tax across the Atlantic.

Chief executive Ian Read said “we have great respect for AstraZeneca and its proud heritage as an innovation-driven biopharmaceutical business with a rich science-based foundation".

He went on to claim that the UK "has created attractive incentives for companies to manufacture products and maintain and protect intellectual property, and we have seen that capital and jobs have followed these types of incentives". Mr Read believes that a potential combination would allow Pfizer "to maintain the flexibility for the potential future separation of our businesses whilst at the same time broadening our pipeline breadth and potential new product launches over coming years".

Just last week, AstraZeneca chief executive Pascal Soriot spoke about the possibility of spin-offs of non-core assets worth up to $15 billion. He also warned about the "disruptive" nature of mergers and it is clear he prefers partnerships to takeovers.

AstraZeneca says it has no comment to make at the moment but is weighing up its response. Investors are getting very excited, however, and the Anglo-Swedish drugmaker's share price has soared this morning, up 14.6% to £46.74 (above Pfizer's original offer) at 9.15am. It promises to be a very interesting week.