Valeant Pharmaceuticals International has taken the unusual step of upping its unsolicited bid to buy Allergan for the second time in a few days.

The company is now offering $72 in cash, up from a bid of $58.30 made in the middle of last week and 0.83 shares of Valeant stock for each Allergan share. The revised offer was triggered by Pershing Square, the hedge fund controlled by Bill Ackman which is Allergan's biggest shareholder with a 9.7% stake, agreeing to take only stock in Valeant for its Allergan shares.

The offer is worth $53.8 billion, up from last week’s $49.9 billion bid. It is subject to “prompt good faith negotiation” of a merger agreement between Valeant and Allergan and again includes a contingent value right sweetener relating to future sales of Allergan's experimental eye drug DARPin.

Mr Ackman noted that he called Valeant chief executive Michael Pearson “and offered to give up $600 million of value to the other Allergan shareholders and exchange our shares for Valeant stock” if the latter increase its offer. He said “we believe that our gesture to the other Allergan owners makes an extraordinarily strong statement about our belief in the long-term value of this highly strategic business combination”, adding that “we look forward to the Allergan board immediately entering into negotiations…and finalising this transaction”.

Messrs Ackman and Pearson may have to wait a while for that to happen as Allergan has shown no desire to engage with Valeant and has been disparaging about the sustainability of the latter’s business model. The Botox maker and eye specialist said it will review the “re-revised proposal”, adding that it had not yet responded to the previous bid from last Wednesday.