The largest drug maker in the United States left its shareholders in the dark when it suddenly pulled out from a bid for AstraZeneca.

The investors are now guessing whether Pfizer will continue going after its rival.

AstraZeneca, UK's leading pharmaceutical company, has been approached by Pfizer four times regarding a possible merger since the beginning of 2014.

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Pfizer CEO Ian Read said after the fourth bid, their final offer reached £55 per share or US$93, which gives a total of £69 billion or US$162 billion value for the AstraZeneca.

When Astra turned down the proposal, Read pulled out his bid saying he was right to be "disciplined" in maintaining a limit for the price of the bid.

Read is getting a lot of criticisms over issuing a "final bid" for Astra, instead of making negotiation and keeping the door open.

Read issued a statement on Tuesday, saying that the decision to make a final offer was supported by Pfizer's shareholders. The investors gave a good feedback regarding the financial discipline that the company observed during the deal, Read said.

Read clarified that Pfizer is looking for a possible company inversion by merging with a company overseas to move its tax bill abroad.

 "When we're looking at AstraZeneca, we look at their pipeline, the synergies and the tax inversion," Read said. Part of the equation they're looking at when considering a merger is the possibility of an inversion since the company has a sizeable balance sheet and financial ability.  

The deal could have been closed id Pfizer's bid was closer to the minimum bid of £59 per share that AstraZeneca wanted, instead of the £55 per share that Pfizer offered.

TagsPfizer, AstraZeneca, busines