The Prime Minister said that he was looking for "more" from the international pharmaceutical company.
For his part Labour leader Ed Miliband said that Pfizer's jobs guarantees, to ensure 20 per cent of the combined company's workforce was based in the UK, were "worthless".
And he called on the Coalition Government to block the takeover if it does not pass a proper test of public interest.
The comments come after Scots-born Pfizer CEO Ian Read spent two days detailing his company's plans to MPs.
Yesterday he used the second session to hit back at AstraZeneca's claim that any takeover could harm patients, by delaying vital new drugs.
"There is absolutely no truth to any comment that some products of critical nature would be delayed getting to patients. If anything we would accelerate that to patients," he told members of the Commons Science and Technology Committee.
Later at Prime Minister's Questions in the Commons Mr Miliband told Mr Cameron that "nobody" was convinced by assurances the Coalition was doing everything it could.
Mr Cameron hit back, accusing the Labour leader of failing to meet the drugs boss, because he was out political campaigning.
"If you think these companies are important, why didn't you meet with them rather than going canvassing?" The Tory leader said.