AbbVie, a Chicago based company, first offered an initial cash and share proposal in early May, valuing Shire at around £39.50 per share.
By their third and final proposal, which was also rejected, their approach represented an indicative offer of £46.26 for each Shire share.
Analysts at Jefferies suggest that there would have been limited product portfolio synergies as the result of a merger, and as a result assume that potential cost savings, tax benefits, and diversification motivated the approach.
A Shire acquisition would likely see AbbVie meet tax inversion criteria, with 20 per cent or more of the combined entities' shareholders being non-US. AbbVie could then benefit from Shire’s favourable tax position and Irish domicile.
At pixel time, Shire shares were more than 14 per cent higher, trading at around £42.72.