AstraZeneca site in Macclesfield
AstraZeneca in MacclesfieldReuters

British drug giant AstraZeneca has again rejected US drugmaker Pfizer's sweetened merger proposal after a review and called the proposal terms as inadequate. AstraZeneca was showing "strong momentum" as an independent company, it added.

"The financial and other terms described in the proposal are inadequate, substantially undervalue AstraZeneca and are not a basis on which to engage with Pfizer," the company said.

"The large proportion of the consideration payable in Pfizer shares and the tax-driven inversion structure remain unchanged. Accordingly, the board has rejected the proposal."

Leif Johansson, chairman of AstraZeneca, added: "Pfizer's proposal would dramatically dilute AstraZeneca shareholders' exposure to our unique pipeline and would create risks around its delivery. As such, the board has no hesitation in rejecting the proposal.

"AstraZeneca continues to invest significantly in research, development and manufacturing in the UK, Sweden and the US. We are showing strong momentum as an independent company, in particular with our exciting, rapidly progressing pipeline, which the board believes will deliver significant value for shareholders."

AstraZeneca had earlier confirmed that it had received an indicative non-binding proposal from Pfizer, which sweetened its offer by about £3bn ($5bn, €3.7bn).

As per the revised terms of the offer, Pfizer will pay £50 per AstraZeneca share in cash and stock, valuing the company at about £63bn.

"The consistent message we have heard reinforces our belief that there is a highly compelling strategic, business and financial rationale for combining our businesses, with significant benefits for shareholders and stakeholders of both companies," said Ian Read, chairman and CEO of Pfizer.

Read also sent a letter to the prime minister David Cameron outlining "Pfizer's commitment to the UK and its life sciences agenda".

On 28 April, both Pfizer and AstraZeneca confirmed media reports that they had discussed a possible merger of the companies in a cash and stock deal, valuing AstraZeneca at £46.61 per share, or £60bn. The merged entity would be incorporated in the UK with headquarters in the US.

AstraZeneca said the terms "significantly undervalued" the company.