A bidding war has broken out to buy Alliance Boots after a rival group said it may table an offer worth £10.8bn.
Boots is one of the UK's most iconic High Street brands.
The proposed bid comes from a group that includes private equity firm Terra Firma, medical charity The Wellcome Trust, and banking group HBOS.
Earlier on Friday, the Boots board backed a £10.6bn takeover bid from Kohlberg Kravis Roberts (KKR) and Boots' deputy boss Stefano Pessina.
Whoever wins, it will be the UK's biggest private equity acquisition.
News of the bidding war sent shares in the High Street chemist and drugs firm up 8.2%, or 86 pence, to £11.35 in London on Friday.
By closing, shares had dropped marginally to close 7% higher at £11.25.
Terra Firma said that there was no guarantee its £11.15 per share proposal - which is conditional on seeing Boots' books - would become a definite offer.
Meanwhile KKR's £10.90 per share move is a firm bid.
A spokesman for KKR told the BBC that "we are fully funded and ready to go".
"We have done our due diligence and in both time value of money and clear strategy for growth we believe our position to be superior to the uncertainties of the other camp," he added.
Customers, suppliers, employees and the unions had to realise that KKR's proposal was "all about growth" and would lead "in the future" to more jobs and significant investments, he argued.
Alliance Boots is best known in the UK for its 2,600 Boots the Chemist shops on the High Street, but it also has 400 overseas outlets in countries including Thailand and Italy.
The group, which was created in a £7bn tie-up with chemist chain Alliance Unichem last year, supplies more than 125,000 pharmacies, health centres and hospitals.
BBC business editor Robert Peston said that the offer from KKR and Mr Pessina was more than had been expected.
In endorsing the KKR bid, Alliance Boots chairman, Sir Nigel Rudd, said he was "delighted that the board has been able to achieve such a good price for shareholders".
"The formation last year of Alliance Boots created a hugely valuable business and this offer reflects that," he added.
KKR first made an approach in early March, but was rebuffed because the offer price was too low.
But the fact that it had the backing of Mr Pessina, Boots' billionaire deputy chairman who already owns 15% of the shares, made it likely the deal would eventually be accepted by the board.
It is thought that Mr Pessina wants to take Boots private to enable it to grow away from the public spotlight.
He said that he and KKR consortium were "committed to accelerating the development of Alliance Boots in order to meet the challenges and opportunities that we face and to build a successful global pharmacy-led healthcare and beauty group."
The offer is 33.7% higher than the price of Boots shares the day before the first approach was made.
A takeover would reignite the debate about whether ownership by private equity was good or bad for British companies, Mr Peston said.
"Unions are bound to complain that there'll be job insecurity for Boots' staff and fat profits for KKR.
"Whereas Stefano Pessina will probably argue that Alliance Boots's prospect for growth would be better as a private company - sheltered from the interference of shareholders and the media."